ST – Solar-Terrestrial Sciences

ST1.1 – Theory and simulation of solar system plasmas

EGU22-307 | Presentations | ST1.1

Joint Instabilities of Sheared Flows and Magnetic Fields

Patrick Lewis, David Hughes, and Evy Kersale

Shear flows and magnetic fields are ubiquitous in astrophysical bodies such as stars and accretion discs. Furthermore,
the interaction between flows and magnetic field plays a key role in the dynamics of plasma fusion devices. Typically,
the flows and magnetic field are both sheared, and it is therefore a problem of fundamental importance to understand
the instabilities that may occur in such a system.

In the absence of magnetic field, the linear stability of a viscous sheared flow is governed by the Orr-Sommerfeld
equation; this is one of the classic problems of hydrodynamics. At the other limit, there are somewhat analogous
instabilities of a fluid of finite electrical conductivity containing a static sheared magnetic field. These are related to
the classical tearing modes that have received considerable attention in both the astrophysical and plasma physics
literature.

In general though, the fluid flow and the magnetic field will both be important players. Previous studies have investigated
configurations which have served as models for systems such as the magnetotail and solar surges. While these
investigations have been fruitful, the prescription of the basic field and flow, while physically motivated, have been
chosen somewhat arbitrarily. It is therefore of interest to consider the instability problem within this more general
framework.

Motivated astrophysically, such as by the dynamics in the solar tachocline, here we consider a self-consistent problem
in which both instabilities can occur. In particular, we consider the stability of equilibrium states arising from the
shearing of a uniform magnetic field by a forced transverse flow. The problem is governed by three non-dimensional
parameters: the Chandrasekhar number, and the flow and magnetic Reynolds numbers. In opposite limits of parameter
space, we recover the predictions of the aforementioned classical problems. As we move through this three-dimensional
parameter space, a range of interactions are possible: We demonstrate the stabilisation of a purely hydrodynamic
instability through the magnetic field, show the existence of a joint instability outlining the physical mechanisms at
play, and demonstrate that under certain conditions, hydrodynamically-stable parallel shear flows lead to instability
growth rates that exceed those of static tearing modes. To conclude, we elucidate the consequences of considering
the linear stability of an evolving background state and show that a quasi-static approach may not be meaningful. In
these circumstances, it therefore becomes essential to perform a stability analysis of a time-varying basic state.

 

 

How to cite: Lewis, P., Hughes, D., and Kersale, E.: Joint Instabilities of Sheared Flows and Magnetic Fields, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-307, https://doi.org/10.5194/egusphere-egu22-307, 2022.

EGU22-1496 | Presentations | ST1.1

Modelling magneto-hydro-static equilibria in quiet Sun regions

Thomas Wiegelmann and Maria Madjarska

The solar magnetic field is measured routinely only
in the solar photosphere. While reliable measurements
of the photospheric magnetic field vector are only available
in active regions, in the quiet Sun at present only
 the vertical component of the magnetic field can be obtained accurately.
 To derive magnetic field structures throughout the solar atmosphere, from
 the chromosphere to the corona, we extrapolate these photospheric measurements
into the upper photosphere, chromosphere and corona with a magneto-hydro-static
model. We optimize free model parameters by comparing the modelled magnetic
field lines with structures observed in solar images. The comparison is
done automatically with a number of quantitative measurements and
the optimal model parameters are found with the help of
a downhill simplex minimization. This newly developed modelling approach can
provide an accurate and deep understanding of the magnetic field structures
that extend to any height in the solar atmosphere.

How to cite: Wiegelmann, T. and Madjarska, M.: Modelling magneto-hydro-static equilibria in quiet Sun regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1496, https://doi.org/10.5194/egusphere-egu22-1496, 2022.

EGU22-1598 | Presentations | ST1.1

Oblique instabilities driven by pickup ion ring-beam distributions in the outer heliosheath

Ameneh Mousavi, Kaijun Liu, and Sina Sadeghzadeh

The energetic neutral atom (ENA) ribbon observed by the Interstellar Boundary Explorer (IBEX) spacecraft is believed to originate from the pickup ions in the outer heliosheath. The outer heliosheath pickup ions generally have a ring-beam velocity distribution at a certain pickup angle, α, the angle at which these ions are picked up by the interstellar magnetic field. The pickup ion ring-beam distributions can drive unstable waves of different propagation angles with respect to the background interstellar magnetic field, θ. Previous studies of the outer heliosheath pickup ion dynamics were mainly focused on ring-like pickup ion distributions with α≈90° and/or the parallel- and anti-parallel-propagating unstable waves (θ=0°and 180°). The present study carries out linear kinetic instability analysis to investigate both the parallel and oblique unstable modes (0°≤θ≤180°) driven by ring-beam pickup ion distributions of different pickup angles between 0° and 90°. Our linear analysis reveals that ring-beam pickup ions can excite mirror waves as well as oblique left-helicity waves and their harmonics. The maximum growth rate of the mirror mode increases with increasing α. On the other hand, the wavenumber and growth rate of the most unstable oblique left-helicity modes are consistent with the unstable modes of 0°and 180° examined in our earlier work.

How to cite: Mousavi, A., Liu, K., and Sadeghzadeh, S.: Oblique instabilities driven by pickup ion ring-beam distributions in the outer heliosheath, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1598, https://doi.org/10.5194/egusphere-egu22-1598, 2022.

EGU22-1705 | Presentations | ST1.1

Characteristic ion length scales for four types of interplanetary shocks

Byeongseon Park, Alexander Pitna, Jana Safrankova, and Zdenek Nemecek

The interaction between interplanetary (IP) shock and solar wind has been studied for the understanding of the energy dissipation mechanism within the collisionless plasma. The power spectra of the magnetic field exhibit breaks, where steepening of these spectra occurs. These breaks have been observed and also regarded as a threshold distinguishing the kinetic range from the inertial range of turbulence. Different heating processes can be related mainly to two characteristic ion length scales — ion inertial length and ion gyroradius. We attempt to establish the relation between these length scales and the spectral break. Data for four different types of IP shocks (fast forwards, fast reverse, slow forwards, slow reverse) measured for 2 hours (one hour for up and downstream plasma) by WIND at 1 AU were used. Continuous wavelet transform for the estimation of the power spectra of measured magnetic field was employed. Spectral breaks were determined by fitting 2-segment piecewise linear function around the expected break position in log-log space. Preliminary analysis of these spectral breaks and the characteristic length scales in fast shocks yields results consistent with the previous studies. Additionally, we extended this analysis towards slow shocks and obtained similar results. While the level of power enhancement of the magnetic field due to fast shocks reaches the order of ten on average, only the order of one was shown for slow shocks. The level of the compression of the characteristic spatial scales, however, is approximately similar for fast and slow shocks.

How to cite: Park, B., Pitna, A., Safrankova, J., and Nemecek, Z.: Characteristic ion length scales for four types of interplanetary shocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1705, https://doi.org/10.5194/egusphere-egu22-1705, 2022.

EGU22-1895 | Presentations | ST1.1

Towards a realistic evaluation of transport coefficients in non-equilibrium plasmas from space

Edin Husidic, Marian Lazar, Klaus Scherer, Horst Fichtner, and Stefaan Poedts

While space plasmas are largely considered to be nearly collisionless, at relatively low heliocentric distances, that is, below 1 AU, particle-particle collisions still play an important role in the transport of matter, momentum, and energy. A way to quantify these processes macroscopically, e.g., in fluid models, is within classical transport theory, where fluxes and their sources are linearly related by transport coefficients. In the solar wind context, of particular interest are the observed velocity distributions of plasma particles with Kappa-distributed suprathermal tails, conditioned not only by binary collisisions, but also by their interaction with plasma waves and turbulence. We present first derivations of the main transport coefficients based on regularised Kappa distributions (RKDs), which, unlike standard Kappa distributions (SKDs), enable a macroscopic description of non-equilibrium plasmas without mathematical divergences or physical inconsistencies. All transport coefficients are finite, well defined for all values of κ > 0, and markedly enhanced in the presence of suprathermal electrons. The results indicate that for low values of κ, that is, below the SKD poles, the transport coefficients can be many orders of magnitudes higher than the corresponding Maxwellian limits, which can lead to significant underestimations if suprathermal electrons are ignored. Moreover, we show the importance of an adequate Kappa modeling of suprathermal populations by contrasting our results to other modified interpretations that underestimate the effects of suprathermals.

How to cite: Husidic, E., Lazar, M., Scherer, K., Fichtner, H., and Poedts, S.: Towards a realistic evaluation of transport coefficients in non-equilibrium plasmas from space, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1895, https://doi.org/10.5194/egusphere-egu22-1895, 2022.

EGU22-2814 | Presentations | ST1.1

Hybrid Particle-In-Cell model with Adaptive Mesh Refinement

Nicolas Aunai, Roch Smets, Philip Deegan, Andrea Ciardi, and Alexis Jeandet

Collisionless magentized plasmas a priori need to be evolved using Vlasov-Maxwell kinetic formalism.
However the tremendous number of spatial and temporal scales involved in phenomena of interest makes it prohibitive, from a computational standpoint.
Fully kinetic particle in cell and single fluid MHD codes are commonly used at very small or very large scales.
The hybrid formalism, treating ions kinetically and electrons as a fluid, is in principle advantageous to fill the gap between these two extremities.
However, a correct treatment of critical regions such as reconnection X-lines require a good resolution of sub-ion dissipative scales, which
still constitute a major challenge if aiming at simulating meso/macro scale systems.
This work presents a new code, named PHARE, which successfully implements the adaptive mesh refinement mechanism in a hybrid particle-in-cell code.
Such a code is able to dynamically focus the resolution in critical regions while others not only have a coarser spatial resolution, but are also
evolved much less often thanks to a recursive time stepping procedure.
Adopting a patch based AMR mechanism, the code architecture is made so that the specific solver/physical model that is solved at a given refined level
is abstracted, thus giving the opportunity to handling multi-formalisms AMR patch hierarchies, where, for instance, coarsest levels are solved in MHD while
dynamicall created refined levels are solved within the Hybrid framework.

How to cite: Aunai, N., Smets, R., Deegan, P., Ciardi, A., and Jeandet, A.: Hybrid Particle-In-Cell model with Adaptive Mesh Refinement, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2814, https://doi.org/10.5194/egusphere-egu22-2814, 2022.

EGU22-2862 | Presentations | ST1.1 | Highlight

The ESA Virtual Space Weather Modelling Centre

Stefaan Poedts and the VSWMC-P3 team

The ESA Virtual Space Weather Modelling Centre (VSWMC) project was defined as a long term project including different successive parts. Parts 1 and 2 were completed in the first 4-5 years and designed and developed a system that enables models and other components to be installed locally or geographically distributed and to be coupled and run remotely from the central system. A first, limited version went operational in May 2019 under the H-ESC umbrella on the ESA SSA SWE Portal. It is similar to CCMC but interactive (no runs on demand) and the models are geographically distributed and coupled over the internet.

The goal of the ESA project "Virtual Space Weather Modelling Centre - Part 3" (2019-2021) was to further develop the Virtual Space Weather Modelling Centre, building on the Part 2 prototype system and focusing on the interaction with the ESA SSA SWE system. The objectives and scope of this new project include maintaining the current operational system, the efficient integration of 11 new models and many new model couplings, including daily automated end-to-end (Sun to Earth) simulations, the further development and wider use of the coupling toolkit  and front-end GUI, making the operational system more robust and user-friendly. The VSWMC-Part 3 project finished recently.

The 11 new models that have been integrated are Wind-Predict (a global coronal model from CEA, France), the Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) model, Multi-VP (another global coronal model form IRAP/CNRS, France), the BIRA Plasma sphere Model of electron density and temperatures inside and outside the plasmasphere coupled with the ionosphere (BPIM, Belgium), the SNRB  (also named SNB3GEO) model for electron fluxes at geostationary orbit (covering the GOES 15 energy channels >800keV and >2MeV) and the SNGI geomagnetic indices Kp and Dst models (University of Sheffield, UK), the SPARX Solar Energetic Particles transport model (University of Central Lancashire, UK), Spenvis DICTAT tool for s/c internal charging analysis (BISA, Belgium), the Gorgon magnetosphere model (ICL, UK), and the Drag Temperature Model (DTM) and operations-focused whole atmosphere model MCM being developed in the H2020 project SWAMI. Many new couplings have also been implemented and a dynamic coupling facility has been installed. Moreover, Daily runs are implemented of two model chains covering the whole Sun-to-Earth domain. The results of these daily runs are made available to all VSWMC users.

We will provide an overview of the state-of-the-art, including the new available model couplings and daily model chain runs, and demonstrate the system.

How to cite: Poedts, S. and the VSWMC-P3 team: The ESA Virtual Space Weather Modelling Centre, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2862, https://doi.org/10.5194/egusphere-egu22-2862, 2022.

The acceleration of high-energy charged particles is common both in heliophysics and astrophysics. Although the diffusive shock acceleration (DSA) has been the well-accepted standard mechanism for particle acceleration at shocks, the fundamental issue is that DSA does not predict the number of accelerated particles. In other words, it relies on an unprescribed injection mechanism that provides a seed population from which the particle acceleration proceeds. Resolving the so-called injection problem is more challenging for electrons than ions because scattering low-energy electrons requires high-frequency waves, which are usually much lower in intensity than low-frequency fluctuations.

 

We have proposed stochastic shock drift acceleration (SSDA) as a plausible electron injection mechanism that can take place within the transition layer of quasi-perpendicular shocks [Katou & Amano, 2019]. The energy gain mechanism of SSDA is essentially the same as the conventional shock drift acceleration (SDA), but the presence of stochastic pitch-angle scattering makes the acceleration more efficient. We will show that the theoretical predictions nicely explain in-situ observations by Magnetospheric MultiScale (MMS) spacecraft [Amano et al. 2020]. Recent fully kinetic Particle-In-Cell (PIC) simulation results will also be shown, in which we found signatures of SSDA [Matsumoto et al. 2017, Kobzar et al. 2021]. We will also present an extended theoretical model that unifies SSDA and DSA. The model predicts a wide range of the energy spectrum from sub-relativistic and relativistic energies. The particle acceleration in the sub-relativistic energy will be dominated by SSDA, which has a spectral index steeper than the standard DSA. Under certain conditions, the particle acceleration mechanism may smoothly transition from SSDA to DSA, and the spectral index approaches the canonical DSA prediction. Therefore, the model can consistently describe the whole particle acceleration process, including the injection by SSDA and the main acceleration to cosmic-ray energies by DSA. We argue that the electron injection scheme through SSDA is realized preferentially at shocks with higher Alfven Mach numbers defined in the Hoffmann-Teller frame.

How to cite: Amano, T.: Electron Injection via Stochastic Shock Drift Acceleration: Theory, Simulation, and Observation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3277, https://doi.org/10.5194/egusphere-egu22-3277, 2022.

EGU22-3304 | Presentations | ST1.1 | Highlight

Recent progress on developments of the magnetohydrostatic extrapolation

Xiaoshuai Zhu, Thomas Wiegelmann, and Bernd Inhester

The magnetohydrostatic (MHS) extrapolation is developed to model the three-dimensional magnetic fields and plasma of the solar atmosphere with the measured vector magnetogram used as boundary condition. It differs from the nonlinear force-free field (NLFFF) extrapolation in that it takes into account plasma forces include pressure gradient and gravity. In this presentation, I will report the recent progress in two aspects on developments of the MHS extrapolation. The first one is the development of a preprocessing method to deal with the non-MHS vector magetograms. The reason of doing this is that there are a small number of the vector magnetograms which are not consistent with the MHS equilibria. The second aspect is the combination of the MHS extrapolation and the NLFFF extrapolation to improve the efficiency of the computation.

How to cite: Zhu, X., Wiegelmann, T., and Inhester, B.: Recent progress on developments of the magnetohydrostatic extrapolation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3304, https://doi.org/10.5194/egusphere-egu22-3304, 2022.

EGU22-3345 | Presentations | ST1.1

Fluid modeling of collisionless plasmas with a non-local kinetic closure

Taiki Jikei and Takanobu Amano

Modeling of collisionless plasmas can be divided into two categories: fluid models and kinetic models. Generally speaking, fluid models require less computational resources than kinetic models, so they are suited for large-scale simulations. However, conventional fluid models such as MHD ignores wave-particle interaction (WPI). It has been pointed out that WPI affects microscopic and macroscopic dynamics and should not be ignored even in MHD scales. This creates a demand for a fluid model of collisionless plasma that takes into account WPI effects.

We have developed a fluid model called the cyclotron resonance closure (CRC) model [1]. The CRC model reproduces linear cyclotron resonance effects using a non-local closure method similar to the Landau closure model. The CRC model reproduces the linear cyclotron resonance and linear growth of ion temperature anisotropy instabilities qualitatively correct. We have also shown that the quasilinear relaxation of temperature anisotropy via resonant waves incorporated in the CRC model.

 Another example of a kinetic fluid model is the well-known Chew-Goldberger-Low (CGL) model. The CGL model is used to analyze low-frequency waves in collisionless plasmas. The CGL model enriched by finite Larmor radius correction and Landau closure predicts the growth rate of firehose instability with reasonable accuracy. However, the CGL model cannot reproduce cyclotron resonance effects such as cyclotron damping and electromagnetic ion cyclotron (EMIC) instability because of the low-frequency assumption.

We will discuss some basic concepts of these kinetic fluid models and their range of application, especially in nonlinear simulation. The CRC model is not limited by frequency (at least up to cyclotron frequency) and can be used for both EMIC and parallel firehose instabilities but need improvement for quantitative agreement with fully kinetic models.

The CGL model can be very accurate in linear analysis of low-frequency waves. We compared the CRC and the CGL model using a simulation of an initially parallel firehose unstable system [2]. We found that the low-frequency approximation of the CGL model fails in some parameters after the appearance of high-frequency oscillation in the nonlinear stage. Also, the absence of cyclotron damping in the CGL model results in a quasi-steady final state that is not consistent with marginal stability analysis.

We conclude that a kinetic fluid model that does not make the low-frequency approximation should be considered instead of the CGL-based approach. The CRC model is a candidate for such a model that can be used in a wide range of parameters.

 

[References]

1. T. Jikei and T. Amano (2021), A non-local fluid closure for modeling cyclotron resonance in collisionless magnetized plasmas, Physics of Plasmas, 28, 042105

2. T. Jikei and T. Amano (2022), Critical comparison of collisionless fluid models: Nonlinear simulations of parallel firehose instability, Physics of Plasmas, Accepted

How to cite: Jikei, T. and Amano, T.: Fluid modeling of collisionless plasmas with a non-local kinetic closure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3345, https://doi.org/10.5194/egusphere-egu22-3345, 2022.

EGU22-3911 | Presentations | ST1.1

Flux tube dependent propagation of Alfvén waves in the solar corona

Chaitanya Prasad Sishtla, Jens Pomoell, Emilia Kilpua, Simon Good, Farhad Daei, and Minna Palmroth
Alfvén wave turbulence has emerged as an important heating mechanism to accelerate the solar wind. The generation of this turbulent heating is dependent on the presence and subsequent interaction of counter-propagating alfvén waves. This requires us to understand the propagation and evolution of alfvén waves in the solar wind in order to develop an understanding of the relationship between turbulent heating and solar wind parameters. In this paper we aim to study the  response  of  the  solar  wind  upon  injecting  monochromatic  single frequency alfvén waves at the base of the corona for various magnetic flux tube geometries. We use an ideal magnetohydrodynamic (MHD) model using an adiabatic equation of state. An alfvén pump wave is injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components. The alfvén waves were found to be reflected due to the development of the parametric decay instability (PDI). Further investigation revealed that the PDI was suppressed both by efficient reflections at low frequencies as well as magnetic flux tube geometries.

How to cite: Sishtla, C. P., Pomoell, J., Kilpua, E., Good, S., Daei, F., and Palmroth, M.: Flux tube dependent propagation of Alfvén waves in the solar corona, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3911, https://doi.org/10.5194/egusphere-egu22-3911, 2022.

EGU22-4064 | Presentations | ST1.1

Mating of two current circuits – A new type of plasma instability

Gerhard Haerendel

In the context of the onset of substorms, observations had revealed the frequent occurrence of an unidentified trigger process. Inspections of such onsets had led to the discovery that high-beta plasma at the magnetosphere-tail boundary became suddenly unstable when so-called auroral streamers lined up closely with that boundary. The manifestation was the appearance of bead-like auroral structures preceding the auroral breakup and subject to nonlinear growth. Highly resolved video coverage of a few events showed that the fast moving beads moved opposite to the convective motions on either side. This led to the proposal [Haerendel & Frey 2021] that the trigger of the instability was the formation of a new current circuit, by a non-MHD process, in the gap between the two adjacent circuits of the high-beta plasma boundary and the auroral streamer. Observational evidence and a model of the current structure will be presented.

How to cite: Haerendel, G.: Mating of two current circuits – A new type of plasma instability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4064, https://doi.org/10.5194/egusphere-egu22-4064, 2022.

EGU22-4892 | Presentations | ST1.1 | Highlight

The 3D Dynamics of Solar Flare Magnetic Reconnection 

Spiro Antiochos, Joel Dahlin, and Richard DeVore

Solar eruptive events (SEE) consisting of a massive filament eruption, intense X-class flare, and a fast CME are the most powerful manifestations of explosive energy release in our solar system and the primary drivers of highly destructive space weather at Earth and in interplanetary space. These giant events, which have global scale of solar radii, allow us to study in great detail fundamental space plasma processes such as magnetic reconnection that are important to many cosmic phenomena. Both 2.5D and 3D numerical simulations have shown that the fast energy release is due to reconnection in a large-scale current sheet that forms in the corona, but the 3D dynamics of the reconnection are far from understood.  The greatest challenge to understanding SEEs is their extreme rate of energy release, and for some events, the amazing efficiency at converting magnetic energy into high-energy particle energy. We present new ultra-high-resolution 3D simulations of flare reconnection using the adaptive-mesh-refinement code ARMS. We find that the reconnection dynamics are dominated by 3D magnetic islands, and show that the islands should have clear observational signatures, especially in the so-called flare ribbons that are commonly observed in the chromosphere. We discuss the central role of the islands for understanding the multiscale coupling at the heart of reconnection, the fast energy release rate, and the high efficiency of particle acceleration.

 

This work was supported by the NASA Living With a Star Program and by the NASA DRIVE Center Program.

 

How to cite: Antiochos, S., Dahlin, J., and DeVore, R.: The 3D Dynamics of Solar Flare Magnetic Reconnection , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4892, https://doi.org/10.5194/egusphere-egu22-4892, 2022.

EGU22-5498 | Presentations | ST1.1

Simulating the FIP effect in coronal loops using a multi-species kinetic-fluid model.

Nicolas Poirier, Michael Lavarra, Alexis Rouillard, Pierre-Louis Blelly, Victor Réville, Andrea Verdini, Marco Velli, Eric Buchlin, and Mikel Indurain

We investigate abundance variations of heavy ions in coronal loops. We develop and exploit a multi-species model of the solar atmosphere (called IRAP’s Solar Atmospheric Model: ISAM) that solves for the transport of neutral and charged particles from the chromosphere to the corona. We investigate the effect of different mechanisms that could produce the First Ionization Potential (FIP) effect. We compare the effects of the thermal, friction and ponderomotive force. The propagation, reflection and dissipation of Alfvén waves is solved using two distinct models, the first one from Chandran et al. (2011) and the second one that is a more sophisticated turbulence model called Shell-ATM. ISAM solves a set of 16-moment transport equations for both neutrals and charged particles. Protons and electrons are heated by Alfvén waves, which then heat up the heavy ions via collision processes. We show comparisons of our results with other models and observations, with an emphasis on FIP biases. This work was funded by the European Research Council through the project SLOW_SOURCE - DLV-819189.

How to cite: Poirier, N., Lavarra, M., Rouillard, A., Blelly, P.-L., Réville, V., Verdini, A., Velli, M., Buchlin, E., and Indurain, M.: Simulating the FIP effect in coronal loops using a multi-species kinetic-fluid model., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5498, https://doi.org/10.5194/egusphere-egu22-5498, 2022.

EGU22-5546 | Presentations | ST1.1 | Highlight

A simulation of flare-driven coronal rain

Wenzhi Ruan, Yuhao Zhou, and Rony Keppens

Coronal rains are cool materials (~10,000 K) that appear at hot corona. They are frequently observed in non-flaring loops of active regions and recently observed in flaring loops at gradual phases. Hot coronal loops (~10 MK) are often produced in flare events due to magnetic reconnection. The hot flare loops gradually recover to typical coronal temperature due to thermal conduction and radiative loss, during which condensation can happen due to thermal instability. Here we demonstrate how the rains formed in a flare loop with a two-and-a-half dimensional magnetohydrodynamic simulation. We simulate a flare event from pre-flare phase all the way to gradual phase and successfully reproduce coronal rains. We find that thermal conduction and radiative losses alternately dominate the cooling of the flare loop. We find that runaway cooling and rain formation also induce the appearance of dark post-flare loop systems, as observed in extreme ultraviolet (EUV) channels.

How to cite: Ruan, W., Zhou, Y., and Keppens, R.: A simulation of flare-driven coronal rain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5546, https://doi.org/10.5194/egusphere-egu22-5546, 2022.

EGU22-5633 | Presentations | ST1.1

Electron cyclotron maser model of solar radio zebras

Jan Benáček and Marian Karlický
Solar radio zebras, occurring as fine structures in radiograms during Type IV bursts, are an excellent tool for plasma diagnostics during solar flares. The main model of zebras is the electron cyclotron maser instability based on double plasma resonance between electron cyclotron and plasma frequencies and an unstable wave in the presence of an unstable type of velocity distribution is necessary, e.g., a loss-cone. The radio emission occurs in the electromagnetic Z-mode along the magnetic field or at the first harmonic of the X-mode in the perpendicular direction. However, it is still unclear where and how the instability evolves and how the locally captured electrostatic waves are converted to escaping radio waves. To obtain the instability evolution, we calculated its growth rates and saturation energies as functions of cyclotron-to-plasma frequency ratio, loss-cone density, cold background  temperature, hot electron thermal velocity, and loss-cone angle by using analytical calculations and particle-in-cell simulations. We found that the growth rates and saturation energies form maxima, approximately located at the harmonic numbers of cyclotron frequency. The maxima shift to lower frequencies with increasing the plasma temperature, they broaden and decrease with increasing the harmonic number. We also estimated electromagnetic energy densities in the emission region and the conversion efficiency to the radio waves.

How to cite: Benáček, J. and Karlický, M.: Electron cyclotron maser model of solar radio zebras, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5633, https://doi.org/10.5194/egusphere-egu22-5633, 2022.

Ubiquitous small-scale vortical motions in the solar atmosphere are thought to play an important role in local heating of the quiet chromosphere and corona. However, an unambiguous method for their detection in observations and numerical simulations has not been found yet.
We aim at developing a robust method for the automated identification of vortices. Local and global rotations in the flow should be considered as both are necessary for the detection of coherent vortical structures. Moreover, the use of a threshold should be avoided to not exclude slow vortices in the identification process.
We present a new method that combines the rigor of mathematical criteria and the global perspective of morphological techniques. The core of the method is the estimation of the center of rotation for every point that presents some degree of local rotation in the flow. For that, we employ the Rortex criterion and the morphology of the neighboring velocity field. We then identify coherent vortical structures by clustering the estimated centers of rotation.
The application of the method to synthetic velocity fields demonstrates its reliability and accuracy. A first statistical study is performed on realistic numerical simulations of the solar atmosphere carried out with the radiative magneto-hydrodynamical code CO5BOLD. We counted on average 0.8 Mm-2 swirls in the photosphere and 1.9 Mm-2 at the bottom of the chromosphere. The average radius varies between 59 km and 72 km. Compared to previous studies, our analysis reveals more and smaller vortical motions in the simulated solar atmosphere. Moreover, we find that 84 % of the swirls in the photosphere show twists in the magnetic field lines compatible with torsional Alfvén waves. 

How to cite: Canivete Cuissa, J. R. and Steiner, O.: An innovative and automated vortex identification method based on the estimation of the center of rotation with application to solar simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5744, https://doi.org/10.5194/egusphere-egu22-5744, 2022.

EGU22-6060 | Presentations | ST1.1

Coronal rain in randomly heated arcades

Xiaohong Li, Rony Keppens, and Yuhao Zhou

Adopting the MPI-AMRVAC code, we present a 2.5-dimensional magnetohydrodynamic simulation, which includes thermal conduction and radiative cooling, to investigate the formation and evolution of the coronal rain phenomenon. We perform the simulation in initially linear force-free magnetic fields that host chromospheric, transition-region, and coronal plasma, with turbulent heating localized on their footpoints. Due to thermal instability, condensations start to occur at the loop top, and rebound shocks are generated by the siphon inflows. Condensations fragment into smaller blobs moving downwards, and as they hit the lower atmosphere, concurrent upflows are triggered. Larger clumps show us clear coronal rain showers as dark structures in synthetic EUV hot channels and as bright blobs with cool cores in the 304 Å channel, well resembling real observations. Following coronal rain dynamics for more than 10 hr, we carry out a statistical study of all coronal rain blobs to quantify their widths, lengths, areas, velocity distributions, and other properties. The coronal rain shows us continuous heating–condensation cycles, as well as cycles in EUV emissions. Compared to the previous studies adopting steady heating, the rain happens faster and in more erratic cycles. Although most blobs are falling downward, upward-moving blobs exist at basically every moment. We also track the movement of individual blobs to study their dynamics and the forces driving their movements. The blobs have a prominence-corona transition-region-like structure surrounding them, and their movements are dominated by the pressure evolution in the very dynamic loop system.

How to cite: Li, X., Keppens, R., and Zhou, Y.: Coronal rain in randomly heated arcades, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6060, https://doi.org/10.5194/egusphere-egu22-6060, 2022.

EGU22-6120 | Presentations | ST1.1 | Highlight

Modeling Reconnection and Turbulence in the Magnetosphere on Kinetic Scales 

Wieslaw M. Macek and Szymon Gorka

We consider magnetic turbulence using observations from the Magnetospheric Multiscale (MMS) mission on kinetic (ions and electron) scales, which are far shorter than the scales characteristic for description of plasma by magnetohydrodynamic (MHD) theory. We have shown that a break of the magnetic spectral exponent to about -5.5 agrees with the predictions of kinetic theory (-16/3), see Ref. [1]. It is worth noting that the unprecedented very high (millisecond) resolution of the magnetic field instrument allowed to grasp the mechanism of reconnection in the magnetotail on kinetic scales, Ref. [2]. As expected from numerical simulations, we have verified that when the field lines and plasma become decoupled a large reconnecting electric field related to the Hall current (1–10 mV/m) is responsible for fast reconnection in the ion diffusion region both at the magnetopause and in the magnetotail regions. Although inertial accelerating forces remain moderate (1–2 mV/m), the electric fields resulting from the divergence of the full electron pressure tensor provide the main contribution to the generalized Ohm’s law at the neutral sheet (of the order of 10 mV/m), cf. [3]. This illustrates that when ions decouple electron physics dominates. The results obtained on kinetic scales may be useful for better understanding the physical mechanisms governing reconnection processes in various magnetized space and laboratory plasmas.

Acknowledgments. This work has been supported by the National Science Center, Poland (NCN), through grant No. 2021/41/B/ST10/00823.

References

1. Macek, W. M., Krasinska, A., Silveira, M. V. D., Sibeck, D. G., Wawrzaszek, A., Burch, J. L., & Russell, C. T. 2018, Magnetospheric Multiscale observations of turbulence in the magnetosheath on kinetic scales, Astrophys. J. Lett., 864, L29, https://doi.org/10.3847/2041-8213/aad9a8.

2. Macek, W. M., Silveira, M. V. D., Sibeck, D. G., Giles, B.L., & Burch, J. L. 2019a, Magnetospheric Multiscale mission observations of reconnecting electric fields in the magnetotail on kinetic scales, Geophys. Res. Lett., 46, 10,295—10,302, https://doi.org/10.1029/2019GL083782.

3. Macek, W. M., Silveira, M. V. D., Sibeck, D. G., Giles, B.L., & Burch, J. L. 2019, Mechanism of reconnection on kinetic scales based on Magnetospheric Multiscale mission observations, Astrophys. J. Lett., 885, L26, https://doi.org/10.3847/2041-8213/ab4b5a.

 

How to cite: Macek, W. M. and Gorka, S.: Modeling Reconnection and Turbulence in the Magnetosphere on Kinetic Scales , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6120, https://doi.org/10.5194/egusphere-egu22-6120, 2022.

EGU22-6171 | Presentations | ST1.1

Two-fluid numerical model towards reproducing the observed solar wave cutoffs.

Błażej Kuźma, Kris Murawski, and Zdzisław Musielak

With use of JOANNA code we developed a numerical model that describes a partially ionized plasma described by a set of two-fluid equations for ion + electron and neutral fluids, coupled by ion-neutral collisions. We used this model to simulate a quiet region of the solar atmosphere with granules spontaneously generated in the photosphere by the underlying solar convective motions. We found that such ongoing granulation excites a wide range of waves propagating into the upper atmospheric layers, with their cutoff frequencies strongly depending on height above the photosphere. We report for the first time numerically obtained cutoff frequencies that are consistent with the cutoff frequencies computed by Stark & Musielak (1993), Kraśkiewicz et al. (2019) and Wójcik et al. (2019). What is even more important, our results remain in agreement with the observational data of Wiśniewska et al. (2016) and Kayshap et al. (2018). As the exact analytical formula for two-fluid cutoff frequencies has not been found up to date, the numerical simulations are crucial tool to answer the ongoing question about impact of different physical processes on cutoffs and their variation in the solar atmosphere.

How to cite: Kuźma, B., Murawski, K., and Musielak, Z.: Two-fluid numerical model towards reproducing the observed solar wave cutoffs., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6171, https://doi.org/10.5194/egusphere-egu22-6171, 2022.

EGU22-6875 | Presentations | ST1.1 | Highlight

Data-Driven MHD Simulations on Magnetic Flux Rope Eruptions

Yang Guo, Mingde Ding, Pengfei Chen, Chun Xia, Rony Keppens, Ze Zhong, Jinhan Guo, and Yiwei Ni

Solar eruptions such as flares and coronal mass ejections could cause disastrous space weather. To understand and predict these eruptive activities, we have to combine multi-wavelength observations and numerical simulations. Recently, data-driven magnetohydrodynamic (MHD) simulations have provided a series of new findings in studying the accumulation of electric current and magnetic energy in active regions, in explaining magnetic flux rope eruptions and coronal mass ejections. We briefly review the progress in this field and introduce one way to realize data-driven MHD simulation, including processing magnetic field observational data, inversion of velocity field and electric field, models as initial conditions and subsequent dynamic simulations. Finally, we will look into the future of the data-driven simulations and point out several methods to improve the simulation results. 

How to cite: Guo, Y., Ding, M., Chen, P., Xia, C., Keppens, R., Zhong, Z., Guo, J., and Ni, Y.: Data-Driven MHD Simulations on Magnetic Flux Rope Eruptions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6875, https://doi.org/10.5194/egusphere-egu22-6875, 2022.

EGU22-7233 | Presentations | ST1.1

Three-dimensional particle-in-cell simulation of high-speed plasma jets interacting with Mercury’s magnetosphere

Gabriel Voitcu, Marius Echim, Eliza Teodorescu, and Costel Munteanu

The transport of high-speed plasma jets (or clouds, streams, blobs, plasmoids) across magnetic discontinuities/shocks is a key process for planetary magnetic environments. Recently, a large number of localized magnetic structures detected in-situ by MESSENGER in the Hermean magnetosheath has been reported in the literature. These structures are similar to the high-speed plasma jets identified in the Earth’s magnetosheath. Due to some limitations in the plasma measurements on-board MESSENGER, only the magnetic signature has been studied. The BepiColombo mission provides a great opportunity to further advance this type of investigation. In this paper we use 3d3v electromagnetic particle-in-cell simulations to study the transport and entry of high-speed plasma jets into Mercury’s magnetosphere. The physical setup is adapted to simulate the kinetic effects and their role on the dynamics of localized plasma structures propagating from the magnetosheath toward the Hermean magnetopause. The magnetospheric field of planet Mercury is provided by the KT17 model, while the high-speed plasma jets are defined as 3D finite-size elements with their bulk velocity pointing towards the dayside magnetopause. We investigate the space and time evolution of the plasma jets prior, during and after their impact on the Hermean magnetopause. We analyse the parallel and perpendicular dynamics with respect to the background magnetic field and emphasize key physical processes for the propagation of high-speed plasma jets across transverse magnetic fields. Our simulations shall support the future exploitation of in-situ data from BepiColombo.

How to cite: Voitcu, G., Echim, M., Teodorescu, E., and Munteanu, C.: Three-dimensional particle-in-cell simulation of high-speed plasma jets interacting with Mercury’s magnetosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7233, https://doi.org/10.5194/egusphere-egu22-7233, 2022.

EGU22-7377 | Presentations | ST1.1

Similarity and difference of Alfvén waves' propagation and evolution in the slow and fast solar wind of inner heliosphere

Jiansen He, Liping Yang, Die Duan, Xingyu Zhu, and Chuanpeng Hou
Parker Solar Probe detected the Alfvénic slow solar wind in the inner heliosphere. Before that, although different spacecraft had measured that slow solar wind sometimes has Alfvénic characteristics, they did not attract extensive and strong attention and discussion. The critical question is, how does the propagation and evolution of Alfvénic waves perform through the same or different processes in the fast and slow solar wind? To study this problem, we simulate the formation of high and low-speed solar wind and the propagation of evolving Alfvén waves therein from a global perspective. Compared with one-dimensional or multi-dimensional simulations with a limited range of latitude and longitude, the advantage of global simulation is that it provides a self-consistent model of fast and slow solar wind coexisting in different flow tubes. Based on this model, we study and evaluate the effects of the expansion, bending, and non-uniformity across the flux tube on the propagation of evolving Alfvén wave. The varying characteristics during the propagation consist of wave amplitude, wave-vector anisotropy, wave mode conversion, etc. As the critical interface to distinguish the sub-Alfvénic and super-Alfvénic solar wind, which is also the vital interface to distinguish the corona and interplanetary space, Alfvén surface is another important aspect of our research. We study the propagation characteristics of Alfvén waves inside and outside the non-spherical interface. In addition, we also discuss the possible relationship between the propagation and evolution of the Alfvén wave and the formation and development of switchback.

How to cite: He, J., Yang, L., Duan, D., Zhu, X., and Hou, C.: Similarity and difference of Alfvén waves' propagation and evolution in the slow and fast solar wind of inner heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7377, https://doi.org/10.5194/egusphere-egu22-7377, 2022.

EGU22-7843 | Presentations | ST1.1

How are the energetics of transverse waves in a coronal loop affected by a transition region?

Timothy Duckenfield, Gabriel Pelouze, and Tom Van Doorsselaere

Transverse waves of a coronal loop, also known as kink waves, are commonplace in the solar atmosphere, both in their standing and propagating form. Such waves may be important in the energy + mass cycles of the solar corona. Furthermore, recent numerical studies of coronal loops have shown that the plasma heating from dissipation of these waves is sufficient to overcome radiative cooling. However, the addition of a dense mass reservoir at the end(s) of the loop in the form of a chromosphere and transition region can alter the energetics of the wave and its evolution compared to a purely coronal loop.
In this talk, I will outline current progress in 3D MHD simulations of a solar loop incorporating a chromosphere, transition region and coronal component in a stratified, thermally conducting atmosphere. Transverse waves are induced from a driver in the chromosphere, showing these waves are able to penetrate the transition region. This result is important for the decay-less oscillation regime, in which very small amplitude transverse oscillations are seen to persist for many periods, despite the (presumable) action of damping mechanisms such as resonant absorption. The fact that decay-less oscillations may be driven down in the chromosphere supports the notion that decay-less oscillations are powered from below.
When the loop is sufficiently driven, the motion of the coronal plasma leads to small scales generated from Kelvin Helmholtz instability eddies, and these deformations are regions of enhanced heating. I will discuss the simulation results on how the wave energy is dissipated into heat; the relationship between the driver and the heating; and the extent to which the entire loop is heated, and compare with the purely coronal case. 

How to cite: Duckenfield, T., Pelouze, G., and Van Doorsselaere, T.: How are the energetics of transverse waves in a coronal loop affected by a transition region?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7843, https://doi.org/10.5194/egusphere-egu22-7843, 2022.

EGU22-8175 | Presentations | ST1.1 | Highlight

The magnetopause discontinuity: a MMS study.

Giulio Ballerini, Gerard Belmont, Laurence Rezeau, and Francesco Califano

The magnetopause boundary seems to escape the general classification of discontinuities since it mixes characteristics of shocks (magnetic field magnitude increase) and those typical for the rotational discontinuities (magnetic rotation), whereas it is very often described as a tangential discontinuity. As, the main issue is the amount of matter/momentum/energy from the solar wind and entering into the magnetosphere, the solution cannot be simply achieved by assuming the discontinuity as strictly tangential, everywhere and at all times. Here we propose to study the magnetopause boundary as a "quasi-tangential" discontinuity, with the normal magnetic component Bn small but not null since even small departures from the standard hypothesis of a zero Bn can lead to noticeable changes in the global properties. In that aim, we look into the MMS database for a large number of magnetopause crossings. For each case we will determine what are the most important features (non-planarity, non-stationarity, Hall effect, pressure anisotropy and agyrotropy) that allow the discontinuity to escape the general classification, i.e. to noticeably change the form of the conservation laws on which the theory of discontinuities is based for non-strictly tangential discontinuities. We put a special emphasis on the refined methods that can be used for determining the spatial gradients from four spacecraft data and on the accuracy that can be attained by these methods.

How to cite: Ballerini, G., Belmont, G., Rezeau, L., and Califano, F.: The magnetopause discontinuity: a MMS study., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8175, https://doi.org/10.5194/egusphere-egu22-8175, 2022.

EGU22-8824 | Presentations | ST1.1

Importance of accurate numerical implementaion of electron inertial terms in hybrid-kinetic simulations  of collisionless plasma turbulence

Neeraj Jain, Patricio A. Muñoz, Jörg Büchner, Meisam Tabriz, and Markus Rampp

A comprehensive understanding of the turbulent dissipation of magnetic energy in collisionless space and astrophysical plasmas, an unsolved problem yet, requires efficient kinetic simulations of collisionless plasma turbulence. Fully kinetic simulations (where all the plasma species, ions and electrons, are treated kinetically) of collisionless plasma turbulence covering a full range of kinetic scales (from ion to electron scales) are computationally demanding.  Hybrid-kinetic simulations (ions treated as kinetic species and electrons as fluid and therefore ignoring electron kinetic effects) with inertia-less electron fluid, although less demanding computationally,  can not address the physics at the electron scales. Hybrid-kinetic simulations with inertial electron fluid are applicable all the way down to electron scales (still ignoring electron kinetic effects) with computational demands in between those for hybrid-kinetic simulations with inertia-less electron fluid and fully kinetic simulations, and, therefore have begun to attract significant interest recently.

The majority of hybrid-kinetic codes, solving either the Vlasov equation for the ions by an Eulerian method (called Vlasov-hybrid codes) or the equations of motion for ion macro-particles by the Lagrangian Particle-in-Cell (PIC) method (called PIC-hybrid codes), numerically implement the electron inertial terms of  the electron fluid equations under varying approximations which are not necessarily valid at electron scales. In hybrid-kinetic codes, electric field is calculated from either the generalized Ohm's law or an elliptic partial differential equation. In the former case, the non-stationary electron inertial term (time derivative of electron bulk velocity) in the generalized Ohm's law is neglected (approximation A1). In the latter case, a part of the electron inertial term involving cross partial derivatives of electric field is  neglected in comparison to the other part involving second order partial derivatives to obtain a simpler elliptic partial differential equation for electric field (approximation A2). For two dimensional collisionless plasma turbulence, we assess the validity of the two approximations of electron inertial terms used in hybrid-kinetic codes for the calculation of electric field. We employ our recently parallelized three-dimensional PIC-hybrid code CHIEF, which numerically implements the electron inertial terms without any of these approximations, in a quasi-two dimensional setup for the simulations of collisionless plasma turbulence.  We find that the approximation A1 impacts the accuracy of the results at the electron scales and therefore may lead to physically incorrect results. Approximation A2, on the other hand, is found to be invalid from ion to electron scales. We conclude that the simulation results obtained using the hybrid-kinetic codes with an approximate numerical implementation of the electron inertial term need to be interpreted with caution.  

How to cite: Jain, N., Muñoz, P. A., Büchner, J., Tabriz, M., and Rampp, M.: Importance of accurate numerical implementaion of electron inertial terms in hybrid-kinetic simulations  of collisionless plasma turbulence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8824, https://doi.org/10.5194/egusphere-egu22-8824, 2022.

EGU22-8919 | Presentations | ST1.1

Modelling the propagation of slow magnetoacoustic waves in a multi-stranded coronal loop

Krishna Prasad Sayamanthula and Tom Van Doorsselaere

The cross-field thermal structure of a coronal loop is one of the critical parameters useful to distinguish the major heating theories. In a recent study we are able to isolate two thermal components of a coronal loop using observations of propagating slow magnetoacoustic waves in two different temperature channels. In order to properly interpret these observations and identify the actual cross-field thermal structure, we develop multiple three-dimensional magnetohydrodynamic models of coronal loop. In each of these models slow magnetoacoustic waves are driven by perturbing the plasma at one end and the corresponding multi-wavelength propagation characteristics are studied by applying forward modelling techniques. We compare the wave propagation properties between different models including a monolithic and a multi-stranded model with those from observations to draw some important inferences which will be discussed in this talk.

How to cite: Sayamanthula, K. P. and Van Doorsselaere, T.: Modelling the propagation of slow magnetoacoustic waves in a multi-stranded coronal loop, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8919, https://doi.org/10.5194/egusphere-egu22-8919, 2022.

EGU22-10585 | Presentations | ST1.1 | Highlight

Properties of cosmic ray test particles in global MHD simulation of the heliosphere

Shuichi Matsukiyo, Kotaro Yoshida, Haruichi Washimi, and Tohru Hada

Heliosphere is a bubble occupied by the solar wind plasma and magnetic field in the local interstellar space. The motion of galactic cosmic rays (GCRs) invading into the heliosphere are strongly affected by the electromagnetic structures of the heliosphere. The statistical behavior of the GCRs near and inside the heliosphere have been conventionally studied by many authors using the diffusion convection model [e.g., Moraal (2013)].

  In this study we investigate the behavior of GCRs invading into the heliosphere in the level of particle trajectory. We conduct test particle simulations of GCRs by using the electromagnetic fields obtained from a global MHD simulation of the heliosphere. The MHD simulation assumes steady solar wind and interstellar wind. GCR protons are initially distributed outside the heliosphere and their motions in the steady virtual heliosphere are calculated by using the Buneman-Boris method. Depending on their initial energy, various types of particle motions, current sheet drift, polar drift, spiral motion, shock drift, Fermi-like acceleration, linear motion, resonantly scattered motion, mirror reflection by bottleneck interstellar field, are observed. We further discuss some statistics of the particles reached at the inner boundary (=50AU from the sun) of the simulation domain.

How to cite: Matsukiyo, S., Yoshida, K., Washimi, H., and Hada, T.: Properties of cosmic ray test particles in global MHD simulation of the heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10585, https://doi.org/10.5194/egusphere-egu22-10585, 2022.

The solar wind has historically been considered as a far simpler medium than the solar or magnetospheric plasma. From the beginning of the space era through to XXI century, it has been supposed that all solar wind structures freely expand and can be modeled in 2D. Correspondingly, current sheets have been pictured as thin planar objects carrying the electric current and separating magnetic fields of different directions. Before 2010th, Petscheck magnetic reconnection was considered as the only possible mechanism transforming the magnetic energy into the thermal energy at current sheets in the solar wind. Acceleration of particles to suprathermal energies was thought to be impossible there because of too slow inflow speeds. Interpretations of observations totally followed the theoretical dominant paradigm mainly because of the insufficiency of observational material. Things began to change when more and more theoretical and observational studies in magnetospheric and solar physics appeared pointing to the complex character of magnetic reconnection. In particular, ideas about stochastic or turbulent reconnection at current sheets in realistic space plasmas become dominating. In turn, observations of the fine structure of current sheets in the solar wind as well as evidence for local acceleration of energetic particles found with help of modern missions, including Parker Solar Probe, allow re-considering views on solar wind current sheets and better understanding physics of the processes associated with magnetic reconnection.   

How to cite: Khabarova, O.: Magnetic reconnection and particle acceleration in the solar wind: theory, observations and opinions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10641, https://doi.org/10.5194/egusphere-egu22-10641, 2022.

EGU22-10807 | Presentations | ST1.1 | Highlight

Homologous Coronal Mass Ejections Caused by Recurring Formation and Disruption of Current Sheet within a Sheared Magnetic Arcade

Chaowei Jiang, Xinkai Bian, and Xueshang Feng

The Sun often produces coronal mass ejections with similar structure repeatedly from the same source region, and how these homologous eruptions are initiated remains an open question. Here, by using a new magnetohydrodynamic simulation, we show that homologous solar eruptions can be efficiently produced by recurring formation and disruption of coronal current sheet as driven by continuously shearing of the same polarity inversion line within a single bipolar configuration. These eruptions are initiated by the same mechanism, in which an internal current sheet forms slowly in a gradually sheared bipolar field and reconnection of the current sheet triggers and drives the eruption. Each of the eruptions does not release all the free energy but with a large amount left in the post-flare arcade below the erupting flux rope. Thus, a new current sheet can be more easily formed by further shearing of the post-flare arcade than by shearing a potential field arcade, and this is favorable for producing the next eruption. Furthermore, it is found that the new eruption is stronger since the newly formed current sheet has a larger current density and a lower height. In addition, our results also indicate the existence of a magnetic energy threshold for a given flux distribution, and eruption occurs once this threshold is approached.

How to cite: Jiang, C., Bian, X., and Feng, X.: Homologous Coronal Mass Ejections Caused by Recurring Formation and Disruption of Current Sheet within a Sheared Magnetic Arcade, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10807, https://doi.org/10.5194/egusphere-egu22-10807, 2022.

EGU22-10833 | Presentations | ST1.1 | Highlight

Can the ultraviolet bursts be generated in the low solar chromosphere? 

Lei Ni

Ultraviolet (UV) bursts and Ellerman bombs (EBs) are small scale magnetic reconnection events in the highly stratified low solar atmosphere. The plasma density, reconnection mechanisms and radiative cooling/transfer process are very different at different atmospheric layers. EBs are believed to form in the up photosphere or low chromosphere. It is still not clear whether UV bursts have to be generated at a higher atmospheric layer than the EBs or UV bursts and EBs can actually both appear in the low chromosphere.   We numerically studied the low beta magnetic reconnection process around the solar temperature minimum region (TMR) by including more realistic physical diffusions and radiative cooling models. We aim to find out if UV bursts can be formed in the low chromosphere and investigate the dominant mechanism that transfer the magnetic energy to heat in an UV burst.The single-fluid MHD code NIRVANA was used to perform simulations. The time dependent ionization degrees of Hydrogen and Helium are included in the code, which lead to the more realistic magnetic diffusion caused by electron-neutral collision and ambipolar diffusion. The more realistic radiative cooling model from Carlsson& Leenaarts 2012 is included in the simulations. The high resolution simulation results indicate that the plasmas in the reconnection region can be heated above 20,000 K as long as the reconnection magnetic fields reach above 500 G, which further proves that UV bursts can be generated in the dense low chromosphere. When the reconnection magnetic fields are stronger than 900 G, the width of the synthesized Si IV 1394 A line profile with multiple peaks can reach above 100 km s-1, which is consistent with the usually observed broad-line-width UV bursts. The dominate mechanism that converts magnetic energy to heat in an UV burst in the low chromosphere is Joule heating that is contributed by magnetic diffusion caused by electron-ion collision in the reconnection region. The average power density that is converted to the thermal energy in the reconnection region is about 100 erg cm-3 s-1, which is comparable to the average power density of the released heat in an UV burst.

 

How to cite: Ni, L.: Can the ultraviolet bursts be generated in the low solar chromosphere? , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10833, https://doi.org/10.5194/egusphere-egu22-10833, 2022.

EGU22-10945 | Presentations | ST1.1

Doppler shifts of spectral lines formed in the solar transition region and corona

Yajie Chen, Hardi Peter, Damien Przybylski, Hui Tian, and Jiale Zhang

Emission lines formed in the transition region and corona show dominantly redshifts and blueshifts, respectively. We investigate the Doppler shifts in a 3D radiation magnetohydrodynamic (MHD) model of the quiet Sun and compare these to observed properties. We concentrate on Si IV 1394 Å originating in the transition region and examine the Doppler shifts of several other spectral lines at different formation temperatures. We construct a radiation MHD model extending from the upper convection zone to the lower corona using the MURaM code. In this quiet Sun model the magnetic field is self-consistently maintained by the action of a small-scale dynamo alone. We synthesize the profiles of several optically thin emission lines, formed at temperatures from the transition region into the corona. We investigate the spatial structure and coverage of red- and blueshifts and how this changes with line-formation temperature. The model successfully reproduces the observed change of average net Doppler shifts from red- to blueshifted from the transition region into the corona. In particular, the model shows a clear imbalance of area coverage of red- vs. blueshifts in the transition region of ca. 80% to 20%, even though it is even a bit larger on the real Sun. We isolate that (at least) four processes generate the systematic Doppler shifts in our model, including pressure enhancement in the transition region, transition region brightenings unrelated to coronal emission, boundaries between cold and hot plasma, and siphon-type flows. We show that there is not the single process that is responsible for the observed net Doppler shifts in the transition region and corona. Because current 3D MHD models do not yet fully capture the evolution of spicules, one of the key ingredients of the chromosphere, most probably these have still to be added to the list of processes responsible for the persistent Doppler shifts.

How to cite: Chen, Y., Peter, H., Przybylski, D., Tian, H., and Zhang, J.: Doppler shifts of spectral lines formed in the solar transition region and corona, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10945, https://doi.org/10.5194/egusphere-egu22-10945, 2022.

The solar magnetic field dominates and structures the
coronal plasma and detailed insights are important to understand almost
all physical processes. While direct routine measurements
of the coronal magnetic field are not available, we have to extrapolate
the photospheric vector field measurements into the corona. To do so,
we developed a new code that performs state-of-the-art nonlinear force-free
magnetic field extrapolations in spherical geometry.
Our new implementation is based on an optimization principle and is
able to reconstruct the magnetic field in the entire corona, including
the polar regions.
Because of the nature of the finite-difference numerical scheme used in
the past, extrapolation close to polar regions was computationally
inefficient. In the current code, the so-called Yin Yang grid is used.
Both the speed and accuracy of the code is improved compared to previous
implementations. We tested our new code with a well known
semi-analytical model (Low and Lou solution). This new Yin and Yang
implementation is timely because
the Solar Orbiter mission is expected to provide reliable
vector magnetograms also in the polar regions within the following years.
Thus, this code can be used in the future when these synoptic magnetograms
are available to model the magnetic field of the solar corona for the entire
Sun including the polar regions.

How to cite: Koumtzis, A. and Wiegelmann, T.: A new global nonlinear force-free coronal magnetic-field extrapolation code implemented on a Yin Yang grid., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11960, https://doi.org/10.5194/egusphere-egu22-11960, 2022.

EGU22-12161 | Presentations | ST1.1 | Highlight

Excitations of Alfven Wave by 3D Patchy and Intermittent Magnetic Reconnection

Liping Yang, Jiansen He, Xueshang Feng, and Ming Xiong

Alfven waves make a central role in energy transfer of the solar atmosphere and heliosphere, with the potential to heat corona, accelerate solar wind, and drive Alfvenic turbulence. It has long been suggested that magnetic reconnection can generate Alfven waves through a relaxation of a highly curved reconnected field lines. Here, with a high-resolution simulation of 3D magnetic reconnection under the solar corona environment, we study this sketch and find that Alfven waves, whose features resemble to those of the Alfven Waves observed in the solar atmosphere, are continually and energetically excited by reconnection mainly through two ways. One involves the current sheet which experiences patchy and intermittent reconnections, and the other refers to the turbulence forming in the outflow regions. The Pointing flux carried by the excited upward-propagating Alfven waves can satisfy the requirements of plasma heating in the corona. This has implications for self-consistent considerations of energy budgets in the solar atmosphere and heliosphere.

How to cite: Yang, L., He, J., Feng, X., and Xiong, M.: Excitations of Alfven Wave by 3D Patchy and Intermittent Magnetic Reconnection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12161, https://doi.org/10.5194/egusphere-egu22-12161, 2022.

EGU22-12196 | Presentations | ST1.1

On the evolution equations of field gradient tensor invariants in MHD Theory

Virgilio Quattrociocchi, Giuseppe Consolini, Massimo Materassi, Tommaso Alberti, and Ermanno Pietropaolo

The understanding of the evolution of turbulence in space plasmas requires the investigation of magnetic field and plasma structures and their time evolution. Indeed, the interactions among different topological multi scale structures have been shown to play an important role tu understand the energy transfer across scales and dissipation. A possible approach to this issue is the study of the geometrical invariants of magnetic and velocity field gradient tensors from a Lagrangian point of view. In the early 1980 a series of works (Vielliefosse, 1982 and 1984) discussed a nonlinear homogeneous evolution equation for the velocity gradient tensor in fluid dynamics.  Here, we derive the evolution equations of the geometrical invariants of the magnetic and velocity field gradient tensors in the case of magneto-hydrodynamic theory and discuss their application to the analysis of magneto-hydrodynamic turbulence in space plasmas.

How to cite: Quattrociocchi, V., Consolini, G., Materassi, M., Alberti, T., and Pietropaolo, E.: On the evolution equations of field gradient tensor invariants in MHD Theory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12196, https://doi.org/10.5194/egusphere-egu22-12196, 2022.

EGU22-12533 | Presentations | ST1.1

MHD wave modes of solar magnetic flux tubes with the realistic cross-section

Anwar Aldhafeeri, Viktor Fedun, Istvan Ballai, and Gary Verth

 

Current and near-future high resolution solar observations indicate that theoretical modelling of the magnetohydrodynamic (MHD) modes in magnetic waveguides with realistic structure and shape now becomes an imperative necessity. 

It was recently shown that even a magnetic structure with elliptical shape, that corresponds to the weak irregularity, may significantly influence the spatial structure of MHD mode in comparison to the mode structure obtained from the modelling which is based on the magnetic flux tube shape with cylindrical cross-section (Aldhafeeri et al., ApJ, 2021). An inaccurate model used for describing waves may lead to the misinterpretation of observational data. 

The expressions for the linear MHD perturbations of a magnetic flux tube are derived by assuming zero value of the vertical component of the velocity perturbation at the boundary of the magnetic flux tube, which is in good agreement with observations. The governing equation for the vertical velocity perturbation was solved by taking into account the observed realistic shape of the sunspot umbra. With these conditions the proposed model is applicable for the analysis of slow body modes under photospheric conditions. 

Our results show that under solar photospheric conditions the conditions of continuity of the component of radial velocity and pressure at the boundary are enough to be imposed, enabling us to use Cartesian coordinates with varsity numerical methods to model the MHD modes with their realistic cross-sectional shape.

 

How to cite: Aldhafeeri, A., Fedun, V., Ballai, I., and Verth, G.: MHD wave modes of solar magnetic flux tubes with the realistic cross-section, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12533, https://doi.org/10.5194/egusphere-egu22-12533, 2022.

EGU22-12904 | Presentations | ST1.1

Three-dimensional Particle-in-Cell (PIC) simulations of non-dipolar minimagnetospheres and comparison to the experiment.

Andrey Divin, Ildar Shaikhislamov, Igor Paramonik, Marina Rumenskikh, Daniil Korovinskiy, and Jan Deca

Magnetospheres are formed when plasma flow interacts with an external source of the magnetic field. Objects (with a size comparable to or less than the ion inertial length or ion gyroradius) formed by relatively weak magnetic field sources are called minimagnetospheres since they are rather different from more common large planetary magnetospheres. 

Moon surface has regions called Lunar Magnetic Anomalies (LMAs) where the remanent magnetization of the Lunar crust provides sources of the magnetic field strong enough to stand off the solar wind. These fields produce minimagnetospheres of the size of the several ion inertial lengths (or gyroradii) or below, typically having weakly structured topology and mostly non-dipolar nature. In this study, we combine numerical simulations and laboratory experiments to investigate ion scattering and basic properties of a non-dipolar minimagnetosphere.  A series of laboratory experiments were carried out on the KI-1 facility (Novosibirsk, Russia) to investigate minimagnetosphere properties for the case of a quadrupolar magnetic field source. The experiment consists of a vacuum chamber, of 5 m length and 1.2 m diameter (with a residual pressure of ~10-7 Torr) filled with a moving plasma. The quadrupolar magnetic field is generated by two coils connected in anti-parallel. The experimental results are supported by the Particle-in-Cell (PIC) three-dimensional simulations using code iPIC3D which capture the full kinetic behavior of the interaction. 

We report several important results based on both the experiment and numerical simulations: 1) a majority of particles is reflected by the Hall electric field formed due to the formation of the magnetopause electron current; however, a hotter portion of the inbound distribution also experiences magnetic deflection closer to the B field source; 2) reflecting electrostatic potential is smaller in the quadrupolar case (if compared to dipolar minimagnetosphere); 3) numerical simulations reproduce well the ion reflection pattern seen in the laboratory experiment, but simulations show slightly less reflected ions which might be attributed to unsteady processes developing during each laboratory run.

How to cite: Divin, A., Shaikhislamov, I., Paramonik, I., Rumenskikh, M., Korovinskiy, D., and Deca, J.: Three-dimensional Particle-in-Cell (PIC) simulations of non-dipolar minimagnetospheres and comparison to the experiment., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12904, https://doi.org/10.5194/egusphere-egu22-12904, 2022.

ST1.5 – Pioneering exploration of the solar corona and near-Sun environment – Latest results from Parker Solar Probe

EGU22-565 | Presentations | ST1.5

Linking In-situ Magnetic and Density Structures in the Low Latitude Slow Solar Wind to Solar Origins

Thomas Woolley, Lorenzo Matteini, Timothy S. Horbury, Stuart D. Bale, Ronan Laker, Lloyd D. Woodham, and Julia E. Stawarz

To date, Parker Solar Probe has completed ten solar encounters and measured a wealth of in-situ data down to heliocentric distances of ~13 solar radii. This data provides a novel opportunity to investigate the near-Sun environment and understand the young slow solar wind. Typically, the slow solar wind observed in the inner heliosphere is split into an Alfvenic and a non-Alfvenic component. The Alfvenic slow wind is thought to originate from overexpanded coronal hole field lines, whereas the non-Alfvenic slow wind could originate from active regions, transient events, or reconnection at the tips of helmet streamers. In this work, we find structures associated with non-Alfvenic slow wind in the low latitude wind measured by Parker Solar Probe. We identify at least two distinct types of structure using magnetic field magnitude, electron pitch angle distributions, and electron number density. After statistically analysing these structures, with a focus on their plasma properties, shape, and location with respect to the heliospheric current sheet, we link them to solar origins. We find structures that are consistent with the plasma blobs seen previously in remote sensing observations.

How to cite: Woolley, T., Matteini, L., Horbury, T. S., Bale, S. D., Laker, R., Woodham, L. D., and Stawarz, J. E.: Linking In-situ Magnetic and Density Structures in the Low Latitude Slow Solar Wind to Solar Origins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-565, https://doi.org/10.5194/egusphere-egu22-565, 2022.

EGU22-1353 | Presentations | ST1.5

Suprathermal Ion Observations Associated with the Heliospheric Current Sheet Crossings during Parker Solar Probe Encounters 7, 8, and 9

Mihir Desai and the the Parker Solar Probe ISOIS, FIELDS & SWEAP Teams

We report observations of <100 keV/nucleon suprathermal (ST) H, He, O, and Fe ions in association with three separate crossings of the heliospheric current sheet that occurred near perhelia during PSP encounters 7, 8, and 9. In particular, we compare and contrast the ST ion time-intensity profiles, velocity dispersion, pitch-angle distributions, spectral forms, and maximum energies during the three HCS crossings. We find that these unique ST observations are remarkably different in each case, with those during E07 posing the most serious challenges for existing models of ST ion production in the inner heliosphere. In contrast, the ISOIS observations during E08 appear to be consistent with a scenario in which ST ions escape out of the reconnection exhausts into the separatrix layers after getting accelerated up to ~50-100 keV/nucleon by HCS-associated magnetic reconnection-driven processes. Finally, ST ions during the E09 HCS crossing have properties that are somewhat similar to those seen during both E07 and E08 crossings, with ion intensities being higher outside the exhausts and the separatrices, but significant intensity increases are also observed inside the reconnection exhausts. We discuss these new observations in terms of local versus remote acceleration sources as well as in terms of expectations of existing ST ion production and propagation, including reconnection-driven and diffusive acceleration in the inner heliosphere.

How to cite: Desai, M. and the the Parker Solar Probe ISOIS, FIELDS & SWEAP Teams: Suprathermal Ion Observations Associated with the Heliospheric Current Sheet Crossings during Parker Solar Probe Encounters 7, 8, and 9, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1353, https://doi.org/10.5194/egusphere-egu22-1353, 2022.

EGU22-1357 | Presentations | ST1.5

Evolution of power spectral density of magnetic field fluctuations in the inner heliosphere

Jana Safrankova, Zdenek Nemecek, Frantisek Nemec, Tereza Durovcova, Luca Franci, and Alexander Pitna

The solar wind is a unique laboratory to study the turbulent processes occurring in a collisionless plasma with high Reynolds numbers. The paper analyzes power spectra of magnetic field fluctuations that are computed in the frequency range around the break between inertial and kinetic scales. We use observations made during first nine Parker Solar Probe encounters and compare them with observations of the spacecraft moving in other distances from the Sun (e.g., Solar Orbiter) and closer to 1 AU (Wind). A preliminary analysis of magnetic field fluctuations based on PSP and Wind measurements from the MHD to kinetic scales has shown that a relative level of compressive fluctuations increases until 0.25 AU and remains constant till 1 AU whereas a relative level of perpendicular fluctuations does not change with the distance from the Sun. We can conclude that the B slope is controlled by different process(es) close to the Sun against 1 AU and that, in spite of expectations, the critical distance for turbulence evolution is as large as 0.25 AU. We also discuss the role of important physical parameters (e.g., ion beta, temperature anisotropy, collisional age, magnetic field fluctuation amplitude) determining the properties of the turbulent cascade in different heliospheric locations.

How to cite: Safrankova, J., Nemecek, Z., Nemec, F., Durovcova, T., Franci, L., and Pitna, A.: Evolution of power spectral density of magnetic field fluctuations in the inner heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1357, https://doi.org/10.5194/egusphere-egu22-1357, 2022.

EGU22-1809 | Presentations | ST1.5

Correlated Magnetic Field Dropouts and Plasma Wave Activity at Switchback Boundaries as Observed by Parker Solar Probe

Anthony Rasca, William Farrell, Robert MacDowall, Stuart Bale, and Justin Kasper

The first solar encounters by the Parker Solar Probe revealed the magnetic field to be dominated by short field reversals in the radial direction referred to as "switchbacks."  While radial velocity and proton temperature were shown to increase inside the switchbacks, B exhibits very brief dropouts only at the switchback boundaries.  Brief intensifications in spectral density measurements near the electron plasma frequency, fpe, have also been observed at these boundaries, indicating the presence of plasma waves triggered by electron beams.  We perform a correlative study using observations from the Parker FIELDS Radio Frequency Spectrometer (RFS) and Fluxgate Magnetometer (MAG) to compare occurrences of spectral density intensifications at the electron plasma frequency (fpe intensifications) and B dropouts at switchback boundaries during Parker's first and second solar encounters.  We find that only a small fraction of minor B dropouts are associated with fpe intensifications.  This fraction increases with B dropout size until all dropouts are associated with fpe intensifications.  This suggests that in the presence of strong B dropouts, electron currents that create the perturbation in B along the boundaries are also stimulating plasma waves such as Langmuir waves.

How to cite: Rasca, A., Farrell, W., MacDowall, R., Bale, S., and Kasper, J.: Correlated Magnetic Field Dropouts and Plasma Wave Activity at Switchback Boundaries as Observed by Parker Solar Probe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1809, https://doi.org/10.5194/egusphere-egu22-1809, 2022.

Helios 1 and 2 data, covering the distance range from 0.3-1au, have been analysed to derive the characteristics of various substructures of interplanetary coronal mass ejections (ICMEs). We have investigated a data sample of 40 events observed by the Helios 1/2 spacecraft during the time period 1974-1981 with respect to the characteristics of different ICME features, such as sheath regions, leading edges and the magnetic ejecta (ME) themselves. For comparison and to investigate events at distances even closer to the Sun, we add a sample of 5 ICMEs observed with Parker Solar Probe during 2018-2021. We study the sheath density variations over distance and relate those to the ambient solar wind speed. The results show that the sheath region is moderately anti-correlated with the solar wind speed ahead of the disturbance. We further find that the sheath density becomes dominant over the ME density beyond about 0.2au and that its spatial extent constantly increases with distance. The results are important for better understanding the CME mass evolution due to sheath enlargements. Based on these analyses we derive an empirical relation between the sheath density and the local solar wind plasma speed upstream of the ICME shock. The empirical results can be used to model the sheath structure and help improve our understanding about CME propagation in the inner heliosphere.

How to cite: Temmer, M. and Bothmer, V.: Sheath characteristics of interplanetary coronal mass ejections derived from Helios and PSP data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2273, https://doi.org/10.5194/egusphere-egu22-2273, 2022.

EGU22-2638 | Presentations | ST1.5

Alfvénicity of velocity and magnetic field Increments Observed by Parker Solar Probe

Panisara Thepthong, Peera Pongkitiwanichakul, and David Ruffolo

Alfvénicity is a well-known property of the solar wind. The magnetic and velocity fluctuations are highly correlated over much of the region between the Sun and the Earth. The Parker Solar Probe (PSP) spacecraft enables us to probe Alfvénicity closer to the Sun than before. One previous finding is that the Alfvén ratio increases as the scales become smaller, as shown in some works by using Fourier analysis. This work measures Alfvénicity from PSP observations using 2nd-order structure functions and other quantities derived from magnetic and velocity increments as functions of time lag. We introduce a method to subtract noise from the velocity structure function. We also provide the relation between a time lag in our work and the frequency that contributes most to the 2nd-order structure function for such a time lag. This relation allows a direct comparison between functions of time lag and Fourier spectra. This research has been supported in part by grant RGNS 63-045 from Office of the Permanent Secretary, Ministry of Higher Education, Science, Research and Innovation, and by grant RTA6280002 from Thailand Science Research and Innovation.

How to cite: Thepthong, P., Pongkitiwanichakul, P., and Ruffolo, D.: Alfvénicity of velocity and magnetic field Increments Observed by Parker Solar Probe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2638, https://doi.org/10.5194/egusphere-egu22-2638, 2022.

The high Reynolds number solar wind flow provides a natural laboratory for the study of turbulence in-situ. Parker Solar Probe has to date executed nine sampling distances between 0.2 AU to 1 AU, providing an opportunity to study how turbulence evolves in the expanding solar wind. We focus on data from the PSP/FIELDS[1] and the PSP/SWEAP[2] experiments which provide magnetic field and plasma observations respectively at sub-second cadence. We have identified multiple intervals of uniform solar wind turbulence, selected to exclude coherent structures such as pressure pulses and current sheets, and in which the primary proton population velocity varies by less than 20% of its mean value. We focus on events of multiple-hour duration, which span the spectral scales from the approximately 1/f range at low frequencies, through the magnetohydrodynamic (MHD) inertial range of turbulence and into the kinetic range, below the ion gyrofrequency. We perform a Haar wavelet decomposition[3] which provides accurate estimations of the exponents of these power-law ranges of the spectra, and of higher-order moments. This allows us to study how the spectral exponents may vary with distance from the sun and with solar wind conditions such as the plasma beta. We perform this analysis for both the magnetic field components and magnitude, which track Alfvenic and compressive turbulent fluctuations, respectively. At 1 AU, compressive fluctuations are known to exhibit scaling properties distinct from that of the individual magnetic field components.[4] Here we will investigate this behaviour at different distances from the Sun, plasma beta, and proton density.

We acknowledge the NASA Parker Solar Probe Mission and the SWEAP team led by J. Kasper and the FIELDS team led by S. D. Bale for use of data.

[1] Bale, S.D., Goetz, K., Harvey, P.R. et al. The FIELDS Instrument Suite for Solar Probe Plus.Space Sci Rev 204, 49–82 (2016). https://doi.org/10.1007/s11214-016-0244-5

[2] Kasper, J.C., Abiad, R., Austin, G. et al. Solar Wind Electrons Alphas and Protons (SWEAP) Investigation: Design of the Solar Wind and Coronal Plasma Instrument Suite for Solar Probe Plus. Space Sci Rev 204, 131–186 (2016). https://doi.org/10.1007/s11214-015-0206-3

[3] Kiyani, K.H., Chapman, S.C., Sahraoui, F., Hnat, B., Fauvarque, O., Khotyaintsev, Y.V.: Enhanced Magnetic Compressibility and Isotropic Scale Invariance at Sub-ion Larmor Scales in Solar Wind Turbulence. The Astrophysical Journal 763(1), 10 (2012). https://doi.org/10.1088/0004-637x/763/1/10

[4] Hnat, B., Chapman, S., Gogoberidze, G., Wicks, R.: Scale-free texture of the fast solar wind. Physical review. E, Statistical, nonlinear, and soft matter physics 84, 065401 (2011). https://doi.org/10.1103/PhysRevE.84.065401
 
 
 
 
 
 

How to cite: Wang, X., Chapman, S., Dendy, R., and Hnat, B.: Wavelet analysis of scaling in plasma fluctuations in the magnetohydrodynamic range of solar wind turbulence seen by Parker Solar Probe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2945, https://doi.org/10.5194/egusphere-egu22-2945, 2022.

EGU22-3195 | Presentations | ST1.5

The emission of near-fce harmonic waves at small radial distances from the Sun

Sabrina F. Tigik, Andris Vaivads, and David M. Malaspina

Near-fce harmonic waves are prevalent in the high-frequency electric field spectrum during Parker Solar Probe's (PSP) close encounters with the Sun. These waves are electrostatic and tend to occur in regions of a relatively stable magnetic field with low broadband magnetic fluctuation levels. We show that the emissions of near-fce harmonic waves are strongly connected to the magnetic field direction. We express the magnetic field direction in terms of spherical angles, where θB is the elevation angle and φB is the azimuthal angle. Then, we show that near-fce harmonics emissions occur when the magnetic field points in a narrow angular range, bounded by 80° ≤ θB ≤ 100° and 10° ≤ φB ≤ 30°, in most of the cases. We also show that the influence of magnetic field direction on near-fce harmonic waves goes down to the shortest time scales the FIELDS instrument can access. These results suggest that cross-scale interaction might play an essential role in the dynamics of the near-fce harmonics measured by PSP at small radial distances from the Sun. It may also provide important clues about the origin of these waves and their role at the early stages of solar wind evolution.

How to cite: F. Tigik, S., Vaivads, A., and M. Malaspina, D.: The emission of near-fce harmonic waves at small radial distances from the Sun, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3195, https://doi.org/10.5194/egusphere-egu22-3195, 2022.

EGU22-3859 | Presentations | ST1.5

Polarization of Langmuir waves observed by RPW-TDS instrument on Solar Orbiter during Type III radio bursts

Jan Soucek, Sampath Bandara, David Pisa, Ondrej Santolik, Milan Maksimovic, Thomas Chust, Yuri Khotyaintsev, Antonio Vecchio, Matthieu Kretzschmar, Robert Wimmer-Schweingruber, Lars Berger, Javier Rodriquez-Pacheco, and Raul Gomez-Herrero

We investigate the polarization of Langmuir waves observed by the Time Domain Sampler (TDS) module of the Radio and Plasma Waves instrument on Solar Orbiter during several extensive Type III burst events. During its two-year-long cruise phase, Solar orbiter often crossed the source region of the Type III radio emission and observed the Langmuir waves generated by solar energetic electrons. The waves are known to exhibit complex modulation and often non-trivial elliptical polarization which sometimes rapidly changes on the timescales of tens of milliseconds. We show that the observed waveforms are typically composed of multiple sub-packets with a relatively short coherence length. We investigate the correlation between the polarization of the waves, simultaneously observed energetic electrons beams and other plasma properties.

How to cite: Soucek, J., Bandara, S., Pisa, D., Santolik, O., Maksimovic, M., Chust, T., Khotyaintsev, Y., Vecchio, A., Kretzschmar, M., Wimmer-Schweingruber, R., Berger, L., Rodriquez-Pacheco, J., and Gomez-Herrero, R.: Polarization of Langmuir waves observed by RPW-TDS instrument on Solar Orbiter during Type III radio bursts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3859, https://doi.org/10.5194/egusphere-egu22-3859, 2022.

EGU22-3917 | Presentations | ST1.5

On the Deflections of Switchbacks

Ronan Laker, Tim Horbury, Lorenzo Matteini, Thomas Woolley, Julia Stawarz, and Stuart Bale

Following their presence during Parker Solar Probe’s (PSP) first encounter, switchbacks have become an active area of research with several proposed mechanisms for their formation. Many of these theories have testable predictions, although it is not trivial to compare simulation results with in-situ data from PSP. For example, there is some debate regarding the deflection direction of switchbacks, with some theories predicting a consistent magnetic deflection in the +T direction in the RTN coordinate system. Such arguments are largely focussed on the first two PSP encounters, as these are the most studied encounters in the literature. We examine the deflection direction of switchbacks for the first eight PSP encounters, with the aim to clear up any ambiguity regarding this property of switchbacks. Much like the earlier results of Horbury et al. 2020 (during the first encounter) we find that switchbacks tend to deflect in the same direction for hours at a time. Although there is some consistency in deflection direction within an individual encounter, crucially we find that there is no preferred deflection direction across all the encounters. We speculate about the cause of these results and what implications they may have for switchback formation theories.

How to cite: Laker, R., Horbury, T., Matteini, L., Woolley, T., Stawarz, J., and Bale, S.: On the Deflections of Switchbacks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3917, https://doi.org/10.5194/egusphere-egu22-3917, 2022.

EGU22-4130 | Presentations | ST1.5

Observations of the Time Domain Sampler receiver from the Radio and Plasma Wave instrument during the Solar Orbiter Earth flyby 

David Pisa, Jan Soucek, Ondrej Santolik, Miroslav Hanzelka, Milan Maksimovic, Antonio Vecchio, Yuri Khotyaintsev, Thomas Chust, Matthieu Kretzschmar, Lorenzo Matteini, and Timothy Horbury

On November 27, 2021, Solar Orbiter completed its only flyby of Earth on its way to the following Sun’s encounter in March 2022. Although this fast flyby was performed primarily to decrease the spacecraft’s velocity and change orbit to get closer to the Sun, the Radio and Plasma Wave (RPW) instrument had the opportunity to perform high cadence measurements in the Earth’s magnetosphere. We review the main observation of the Time Domain Sampler (TDS) receiver, a part of the RPW instrument, made during this flyby at frequencies below 200 kHz. The TDS receiver operated in a high cadence mode providing us with the regular waveform snapshot with 62 ms length every ten seconds for two electric components. Besides the regular captures, we have got more than five hundred onboard classified snapshots and the statistical products with a sixteen-second cadence. Before entering the terrestrial magnetosphere around 02:30UT, the spacecraft wandered through the foreshock region, registering intense bursts of Langmuir waves. After the bowshock crossing, Solar Orbiter was for more than two hours in the morning sector of the magnetosphere, recording various plasma wave modes. The closest approach was reached at 04:30UT above North Africa at an altitude of 460 km. Then the spacecraft continued into the Earth’s tail and entered the magnetosheath around 13:00UT. After 15:00UT, the Solar Orbiter crossed the bowshock, and bursts of Langmuir waves were detected again pointing out to the deep downstream foreshock region. Further from the Earth, intense Auroral Kilometric Radiation (AKR) at frequencies above 100 kHz was also detected.

How to cite: Pisa, D., Soucek, J., Santolik, O., Hanzelka, M., Maksimovic, M., Vecchio, A., Khotyaintsev, Y., Chust, T., Kretzschmar, M., Matteini, L., and Horbury, T.: Observations of the Time Domain Sampler receiver from the Radio and Plasma Wave instrument during the Solar Orbiter Earth flyby , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4130, https://doi.org/10.5194/egusphere-egu22-4130, 2022.

EGU22-8923 | Presentations | ST1.5

Origin of the solar wind observed by PSP 

Jasmina Magdalenic, Senthamizh Pavai Valliappan, and Luciano Rodriguez

The recently available novel Parker Solar Probe (PSP) observations allow mapping of the solar wind characteristics in the low solar corona, at only a few tens of solar radii, and study the characteristics of the solar wind and its transients close to the Sun. The first few perihelion passes of the PSP revealed the highly variable structure of the solar wind. These observations provided the unique possibility to study the solar wind originating from small coronal holes. Such studies were previously not possible as the majority of the in situ observations were taken at distances of about 1 AU, and the association of the solar wind originating from the small coronal holes and its sources on the Sun was extremely unreliable. We employ a magnetic connectivity tool (developed by ESA’s MADAWG group) to associate the solar wind parcels observed by the PSP with their source regions on the Sun.  Our study encompasses the first eight PSP perihelion passes, using a time window of about three weeks around each perihelion. The first results indicate that we can well distinguish and identify the solar wind observed by the PSP originating not only from the big, but also from the small coronal holes.

How to cite: Magdalenic, J., Valliappan, S. P., and Rodriguez, L.: Origin of the solar wind observed by PSP , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8923, https://doi.org/10.5194/egusphere-egu22-8923, 2022.

EGU22-8932 | Presentations | ST1.5

Solar wind modelling with EUHFORIA and comparison with the PSP observations

Senthamizh Pavai Valliappan, Jasmina Magdalenic, Luciano Rodriguez, Stefaan Poedts, and Evangelia Samara

During recent decades, numerous studies were devoted to improve our understanding of the origin and the propagation of the fast solar wind, and its accurate modelling. The solar wind characteristics were poorly mapped up to now by the in situ observations, available mostly only at about 1AU. The novel Parker Solar Probe (PSP) observations, that are employed in this study, allow us to map the solar wind characteristics in the low solar corona at only few tens of solar radii, and to study the solar wind characteristics. These observations are also very important for understanding how accurately we can model the solar wind characteristics employing models such as EUHFORIA (European heliospheric forecasting information asset, Pomoell & Poedts, 2018), at distances rather close to the Sun.
In this study, we inspect the solar wind characteristics during the first eight closest PSP approaches to the Sun. The solar wind plasma characteristics observed by PSP are compared with the modelling results using the default set-up of EUHFORIA. We also calibrate the inner boundary (0.1 AU) conditions in EUHFORIA, but without changing the Wang-Sheeley-Arge formula which describes the solar wind characteristics at the inner boundary. The aim is to better model the solar wind at distances close to the Sun. We also use a magnetic connectivity tool (developed by ESA’s MADAWG group) to better associate the fast solar wind with its source region on the Sun.

How to cite: Valliappan, S. P., Magdalenic, J., Rodriguez, L., Poedts, S., and Samara, E.: Solar wind modelling with EUHFORIA and comparison with the PSP observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8932, https://doi.org/10.5194/egusphere-egu22-8932, 2022.

EGU22-9673 | Presentations | ST1.5

From Magnetic Reconnection at Chromospheric Network Boundaries to Switchbacks in the Inner Heliosphere

Chuanpeng Hou, Jiansen He, Die Duan, Huichao Li, and Yajie Chen

During its perihelion encounter, Parker Solar Probe (PSP) has observed abundant kink and switchback patterns of magnetic field lines in the young solar wind. Such switchback structures have gained widespread attention due to their manifestation of Alfvenic and compressional properties, such as velocity enhancement, plasma density, and temperature variation. In particular, the origin mechanism has been a hot topic and waits to be observationally confirmed. Here we use a two-step ballistic backmapping method (tracing along the Parker Spiral and the PFSS-solution extrapolated from the GONG synoptic magnetogram) to determine the foot-points of the magnetic lines during switchback events measured by PSP on 24th-27th Jan. 2020. We identify ten jets corresponding to the PSP-switchbacks and find relevance between jets and switchback patches. We find that jets excite at the height of around low corona and position of chromospheric network boundaries. About 70% of jets accompany a magnetic cancelation, while 30% of jets are related to magnetic emergence. The variation in magnetic flux corresponding to magnetic cancelation and magnetic emergence is quantitatively equal to that of radial magnetic flux associated with switchback patches. These features suggest that switchbacks may originate from an interchange magnetic reconnection at chromospheric network boundaries, which provides direct evidence of switchbacks' solar origin. 

How to cite: Hou, C., He, J., Duan, D., Li, H., and Chen, Y.: From Magnetic Reconnection at Chromospheric Network Boundaries to Switchbacks in the Inner Heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9673, https://doi.org/10.5194/egusphere-egu22-9673, 2022.

EGU22-12654 | Presentations | ST1.5

Non-thermal features in proton and alpha velocity distribution functions in the solar wind in the inner heliosphere

Raffaella DAmicis, Roberto Bruno, Rossana De Marco, Marco Velli, Daniele Telloni, Denise Perrone, Luca Sorriso-Valvo, and Olga Panasenco

The solar wind is a highly variable, weakly collisional plasma originating from the Sun. The recent launches of PSP and Solar Orbiter have opened the way for the exploration of the innermost regions of our solar system and will greatly advance our understanding of several plasma phenomena occurring in the near-Sun environment, such as the heating and the acceleration of the solar wind. 

Plasma waves and wave-particle interactions play a relevant role in such phenomena, determining significant deviations of the Velocity Distribution Function (VDF) from the Local Thermodynamic Equilibrium. These deviations retain information of the interaction of particles with the turbulent electromagnetic fields and can be identified as thermal anisotropy, or non-thermal ion beams and heavy ion differential streaming in the ion component of the solar wind. This study will cover these topics with particular reference to new in-situ data from Solar Orbiter, PSP and with observations at L1  (e.g. Wind), with a focus on the central role Alfvénic fluctuations play in the evolution of the VDF features mentioned above.

How to cite: DAmicis, R., Bruno, R., De Marco, R., Velli, M., Telloni, D., Perrone, D., Sorriso-Valvo, L., and Panasenco, O.: Non-thermal features in proton and alpha velocity distribution functions in the solar wind in the inner heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12654, https://doi.org/10.5194/egusphere-egu22-12654, 2022.

ST1.6 – The neutron monitor network: challenges and future perspective

EGU22-13123 | Presentations | ST1.6

Galactic cosmic rays as signatures of interplanetary transients

Mateja Dumbovic

Coronal mass ejections (CMEs), interplanetary shocks, and corotating interaction regions (CIRs) drive heliospheric variability, causing various interplanetary as well as planetary disturbances. One of their very common in-situ signatures are short-term reductions in the galactic cosmic ray (GCR) flux (i.e. Forbush decreases), which are measured by ground-based instruments at Earth and Mars, as well as various spacecraft throughout the heliosphere (most recently by Solar Orbiter). In general, interplanetary magnetic structures interact with GCRs producing depressions in the GCR flux. Therefore, different types of interplanetary magnetic structures cause different types of Forbush decreases, allowing us to distinguish between them. With new modelling efforts, as well as observational analysis we are one step closer in utilizing GCR measurements to provide information on interplanetary transients, especially where other measurements (e.g. plasma, magnetic field) are lacking.

How to cite: Dumbovic, M.: Galactic cosmic rays as signatures of interplanetary transients, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13123, https://doi.org/10.5194/egusphere-egu22-13123, 2022.

EGU22-4352 | Presentations | ST1.6

Diurnal Dips and Forbush Decreases in Galactic Cosmic Rays Observed at High Cutoff Rigidity

Chanoknan Banglieng, David Ruffolo, Alejandro Sáiz, Warit Mitthumsiri, Tanin Nutaro, Marc L. Duldig, and John E. Humble

A Forbush decrease (FD) is the decrease in Galactic cosmic ray (GCR) flux, e.g., as observed by a neutron monitor count rate, in association with a coronal mass ejection (CME) and/or its shock. The FD amplitude is known to decrease at higher cutoff rigidity. During Solar Cycle 24, the Mawson neutron monitor in Antarctica, with a low (atmosphere-limited) cutoff rigidity of ~1 GV, observed numerous FDs, while the Princess Sirindhorn Neutron Monitor (PSNM) located near the Earth's equator at Doi Inthanon, Thailand, with the world’s highest geomagnetic cutoff rigidity (17 GV), observed only a fraction of these as FDs.  Instead, we find that the shock arrival is often followed by repeated dips in the PSNM count rate at only certain times of day, while the GCR flux from other directions remains near the pre-shock level.  We refer to decreases of this type as diurnal dips.  In this work, we have surveyed FDs and diurnal dip events observed by PSNM and the dependence of their maximum amplitude on the solar wind speed, ICME speed, and interplanetary magnetic field.  We acknowledge logistical support from Australia's Antarctic Program for operating the Mawson NM and support from the National Astronomical Research Institute of Thailand and grant RTA6280002 from Thailand Science Research and Innovation.

How to cite: Banglieng, C., Ruffolo, D., Sáiz, A., Mitthumsiri, W., Nutaro, T., Duldig, M. L., and Humble, J. E.: Diurnal Dips and Forbush Decreases in Galactic Cosmic Rays Observed at High Cutoff Rigidity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4352, https://doi.org/10.5194/egusphere-egu22-4352, 2022.

EGU22-1221 | Presentations | ST1.6

Diurnal anisotropy of polar neutron monitors, Dome C looks poleward

Agnieszka Gil, Alexander Mishev, Stepan Poluianov, and Ilya Usoskin

Galactic cosmic rays (GCR) show a small local anisotropy detected as a diurnal variability of neutron monitor (NM) count rates. As the asymptotic directions of different NMs are diverse, the capability of the GCR diurnal variation observation is also various. Here we present that the Dome C (DOMC) NM is barely sensitive to the diurnal variation. Its amplitude is very small, 0.03%, in comparison to other polar NMs, for which the diurnal variability amplitudes vary from 0.16 to 0.4%. This fact is associated to the narrow asymptotic-direction cone of DOMC NM looking almost to the South pole with geographic latitude above 75o. Thus, DOMC NM is the only existing NM accepting cosmic-ray particles from the off-equatorial region, which makes this station a unique detector.

How to cite: Gil, A., Mishev, A., Poluianov, S., and Usoskin, I.: Diurnal anisotropy of polar neutron monitors, Dome C looks poleward, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1221, https://doi.org/10.5194/egusphere-egu22-1221, 2022.

EGU22-10415 | Presentations | ST1.6

Scaling features of cosmic rays, solar, heliospheric and geomagnetic data

Renata Modzelewska, Agata Krasińska, Anna Wawrzaszek, and Agnieszka Gil

EGU22-11343 | Presentations | ST1.6

Characteristics of a long-lived CIR and analytical modelling of the corresponding depression in the GCR flux

Mateja Dumbovic, Bojan Vrsnak, Bernd Heber, Manuela Temmer, Patrick Kuhl, and Anamarija Kirin

We observe a long-lived CIR recurring in 27 consecutive Carrington rotations 2057-2083 in the time period from June 2007 - May 2009. We characterize the in situ measurements of this long-lived CIR as well as the corresponding depression in the GCR count observed by SOHO/EPHIN, and analyze them throughout different rotations. We find that the inverted GCR count time-profile correlates well with that of the flow speed throughout different rotations. We perform a statistical analysis and find the GCR count amplitude correlated to the peak in the magnetic field and flow speed, as expected based on previous statistical studies. In order to characterize a generic CIR profile for modelling purposes, we perform the superposed epoch analysis using relative values of the key parameters. Based on the observed properties we propose a simple analytical model starting from the basic Fokker-Planck equation. We employ a convection-diffusion GCR propagation model and apply it to the solar wind and interplanetary magnetic field properties observed for the analyzed long-lived CIR. Our analysis demonstrates a very good match of the model results and observations.

How to cite: Dumbovic, M., Vrsnak, B., Heber, B., Temmer, M., Kuhl, P., and Kirin, A.: Characteristics of a long-lived CIR and analytical modelling of the corresponding depression in the GCR flux, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11343, https://doi.org/10.5194/egusphere-egu22-11343, 2022.

EGU22-11286 | Presentations | ST1.6

Integral fluences of GLEs: A new full reconstruction

Ilya Usoskin, Sergey Koldobskiy, and Gennady Kovaltsov

For many reasons, from solar physics to terrestrial and engineering applications, it is important to estimate the total fluences of solar energetic particles (SEPs) especially for the strongest hard-spectrum events known as ground-level enhancements (GLEs). Here we present a revised reconstruction of the SEP spectral fluences using a recently developed probabilistic Monte-Carlo method, applied to major GLE events of the last decades. The method utilizes data from the ground-based neutron-monitor network in the higher-energy range and revised space-borne/ionospheric data for the lower-energy part. The fluences are reconstructed along with realistic uncertainty estimates which appear large for weak events and small for strong events.

How to cite: Usoskin, I., Koldobskiy, S., and Kovaltsov, G.: Integral fluences of GLEs: A new full reconstruction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11286, https://doi.org/10.5194/egusphere-egu22-11286, 2022.

The first solar proton event of solar cycle 25 was detected on 28 October 2021 by several neutron monitors (NMs) in the polar regions, the strongest signal was registered by the DOMC/DOMB monitors located at the Antarctic plateau at Concordia French-Italian research station. It is identified as the GLE (ground-level enhancement) #73 in the International GLE database. Here, we report the observations of the GLE by the global NM network and present the derived angular and spectral features of solar energetic protons with their dynamical evolution throughout the event employing a state-of-the-art model based on analysis of the neutron monitor data. Using the derived spectra we computed the related terrestrial effects, namely the cosmic rate induced ionization at several altitudes on a global map and discuss possible implications.

How to cite: Mishev, A., Larsen, N., and Usoskin, I.: The first GLE (# 73 – 28-Oct-2021) of solar cycle 25: a study of the related terrestrial effects using neutron monitor data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1243, https://doi.org/10.5194/egusphere-egu22-1243, 2022.

EGU22-5504 | Presentations | ST1.6

Characteristics of the First Ground Level Enhancement (GLE) of Solar Cycle 25 on 28 October 2021

Athanasios Papaioannou, Athanasios Kouloumvakos, Alexander Mishev, Rami Vainio, Ilya Usoskin, Konstantin Herbst, Alexis P. Rouillard, Anastasios Anastasiadis, Jan Giesler, Robert Wimmer-Schweingruber, and Patrick Kuhl

We present an overview of the first ground-level enhancement (GLE) event of solar cycle 25, recorded on 28 October 2021 (GLE73), based on the available neutron monitor (NM) network observations and on data from near-Earth spacecraft (GOES, SOHO, SolO). The maximum increase was ~7.3% for DOMC (Dome C NM at Concordia station) and 5.4% for SOPO (South Pole) conventional NMs located on the Antarctic plateau. Bare (lead-free) NMs at the same sites detected a higher response (14.0% for DOMB and 6.6% for SOPB). The Fort Smith (FSMT) NM shows the earliest increase among the high-latitude NMs, indicating a moderate anisotropy in the first phase of the GLE event. The maximum rigidity of accelerated protons did not exceed 2.4 GV. We estimated the solar release time (SRT) of ≥1 GV protons into open magnetic field lines at ~15:40 UT.  In-situ proton observations from near-Earth spacecraft were combined with the detection of a solar flare in soft X-rays (SXRs), a coronal mass ejection (CME), radio bursts and extreme ultraviolet (EUV) observations to identify the solar origin of the GLE. Around the ≥1 GV proton SRT the CME-driven shock was located at a height of ~2.33 Rs. The timing of the EUV wave evolution towards the field lines magnetically connected to Earth seem to be in good agreement with the inferred release time of ≥1 GV protons.

How to cite: Papaioannou, A., Kouloumvakos, A., Mishev, A., Vainio, R., Usoskin, I., Herbst, K., Rouillard, A. P., Anastasiadis, A., Giesler, J., Wimmer-Schweingruber, R., and Kuhl, P.: Characteristics of the First Ground Level Enhancement (GLE) of Solar Cycle 25 on 28 October 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5504, https://doi.org/10.5194/egusphere-egu22-5504, 2022.

EGU22-4215 | Presentations | ST1.6

Cosmic Ray Flux Correlation between McMurdo and Jang Bogo Neutron Monitor Stations vs. Time Lag

Ekawit Kittiya, Waraporn Nuntiyakul, Achara Seripienlert, Paul Evenson, Alejandro Saiz, David Ruffolo, and Sueyon Oh

A neutron monitor is a large ground-based detector responding to the flux of cosmic ray particles in space by measuring atmospheric secondary neutrons. Any ground-based detector is sensitive to cosmic rays from a specific range of directions in space. In particular, a particle arriving from a specific sky direction with a specific rigidity (momentum per unit charge) was necessarily moving from a certain direction in space, called the asymptotic direction. McMurdo and Jang Bogo neutron monitor stations are Antarctic stations with similar geomagnetic latitudes but slightly different longitudes. From December 17, 2015 to January 9, 2017, six of the eighteen neutron counters from McMurdo had been transferred to Jang Bogo (with full transfer to Jang Bogo completed in December 2017). We present an analysis of the correlation of the cosmic ray flux between the McMurdo and Jang Bogo stations, during the time when both were operating, with ten-second time resolution. Although highly correlated, there are significant differences, including a systematic time lag of approximately 16 minutes between the data from the two stations. Although McMurdo observes with similar asymptotic directions to Jang Bogo, the response-weighted average directions still have a substantial difference of 21.9 degrees in geographic longitude, so with Earth’s rotation, time-independent anisotropy effects should induce a lag of 88 minutes.  Because the observed lag of 16 minutes is intermediate between 0 and 88 minutes, the joint observations reveal structure in the interplanetary cosmic-ray density that is consistent with a combination of simultaneous temporal variations and non-simultaneous variations with direction (i.e., anisotropy). The research is supported in part by a TA/RA scholarship (active recruitment) of Chiang Mai University and Thailand Science Research and Innovation via Research Team Promotion Grant RTA6280002.

How to cite: Kittiya, E., Nuntiyakul, W., Seripienlert, A., Evenson, P., Saiz, A., Ruffolo, D., and Oh, S.: Cosmic Ray Flux Correlation between McMurdo and Jang Bogo Neutron Monitor Stations vs. Time Lag, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4215, https://doi.org/10.5194/egusphere-egu22-4215, 2022.

EGU22-13288 | Presentations | ST1.6

Measuring neutron monitor multiplicities at SANAE

Du Toit Strauss

We present new results of the neutron monitor (NM) multiplicity, as measured by the SANAE NM with updated electronics, down to 10 microseconds. We identify the high-multiplicity component, formed when high-energy particles interact with the NM and produce multiple neutrons in the lead producer. This component is absent in the lead-free monitors and is absent when testing the leaded NM with a low-energy neutron source. We study the pressure dependence of both the high- and low-multiplicity components, as well as the ratio thereof. We show how this ratio, as a proxy for the energy spectrum of atmospheric particles incident on the NM, changes during a relatively small Forbush decrease observed in November 2021.

How to cite: Strauss, D. T.: Measuring neutron monitor multiplicities at SANAE, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13288, https://doi.org/10.5194/egusphere-egu22-13288, 2022.

EGU22-5650 | Presentations | ST1.6

Coincident signals on multiple counters in a neutron monitor: Sparse vs. dense atmospheric secondary particles from cosmic ray showers 

Kullapha Chaiwongkhot, David Ruffolo, Poompong Chaiwongkhot, Alejandro Sáiz, and Chanoknan Banglieng

Neutron monitors were designed to measure atmospheric secondary neutrons from cosmic ray showers in order to track the cosmic ray flux vs. time.  Furthermore, at the Princess Sirindhorn Neutron Monitor (PSNM), an 18-counter NM64 detector at 2560-m altitude at Doi Inthanon, Thailand, the leader fraction (inverse multiplicity) inferred from time delay distribution between successive neutron events in the same counter has been used to track spectral variations.  More recent measurements of time delays between neutron events in different counters, as a function of counter separation, have confirmed that 1) the product neutrons from the interaction of a single atmospheric secondary neutron can spread among neighboring counters, with a cross-counter leader fraction that depends on whether the first counter is an end or middle counter, and 2) coincident counts between distant counters can be produced by multiple atmospheric secondary neutrons from the same primary cosmic ray, with a leader fraction that depends on whether the second counter is an end or middle counter.  Here we report on measurements of neutron signals in amplifier outputs at PSNM using a 4-channel oscilloscope, in order to further investigate these phenomena.  For a pair of neighboring counters located at the edge of the counter array, we find roughly equal event rates in either neighbor following a neutron trigger in one of them, implying that the difference in leader fraction relates to the base count rate of the first counter and is therefore lower if that is an end counter. In addition, an FPGA-based readout system was developed for more efficient collection of neutron events on two distant counters (Tubes 2 and 18) that were coincident within a 250-microsecond time window, while also monitoring Tube 10 in between.  The time distributions and neutron multiplicities indicate that a small fraction of the cosmic ray events that triggered both Tubes 2 and 18 also led to neutron events on Tube 10 with an enhanced rate of high multiplicity, indicating a few air shower events that densely “carpeted” the neutron monitor, while the majority of such coincidences apparently involved a sparse distribution of isolated secondary particles near Tube 2 and near Tube 18 and not near the intermediate Tube 10, which is consistent with a cross-counter leader fraction dependence on the count rate of the second counter.  This research was supported by the postdoctoral research sponsorship of Mahidol University, Thailand, by grant RTA6280002 from Thailand Science Research and Innovation, and by grant NSRF from the Program Management Unit for Human Resources & Institutional Development, Research and Innovation, NXPO, Thailand [grant number B05F640051]. 

How to cite: Chaiwongkhot, K., Ruffolo, D., Chaiwongkhot, P., Sáiz, A., and Banglieng, C.: Coincident signals on multiple counters in a neutron monitor: Sparse vs. dense atmospheric secondary particles from cosmic ray showers , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5650, https://doi.org/10.5194/egusphere-egu22-5650, 2022.

EGU22-5376 | Presentations | ST1.6

Boron-coated straw detector technology as an alternative to helium-3 and boron trifluoride based proportional counters for ground level neutron monitoring: a design study.

Michael Aspinall, Cory Binnersley, Steve Bradnam, Stephen Croft, Malcolm Joyce, Lee Packer, and Jim Wild

The global network of neutron monitors comprises predominantly of the monitor standardised by Carmichael in 1964, the NM-64.  The design of these existing monitors and their instrumentation have changed very little over the last sixty years.  For example, their neutron detectors rely on gas filled proportional counters that are either filled with highly toxic boron trifluoride (BF3) or helium-3 (3He).  Almost the entire global supply of 3He is derived from a waste product of nuclear weapons programmes and, with the termination of such programmes and reducing nuclear weapons stockpile, the supply of 3He has become limited.  Consequently, 3He supply became strictly controlled in 2008 and its price has fluctuated since.  In some cases, new neutron monitors have reverted to BF3 filled counter tubes when the price of 3He has been at a premium.  Helium-3 filled proportional counters are also used extensively in radiation portal monitors deployed for homeland security and non-proliferation; objectives which have increased significantly over the last two decades.  The reduced production and increased demand for 3He has led to concerns over its supply and provided the research motivation for alternative neutron detection methods which are viable in terms of sensitivity, stability and gamma-rejection for certain applications.  One of these alternative technologies is based on boron-coated straws (BCS) manufactured and supplied by Proportional Technologies, Inc (PTI).  The technology is built on a patented low-cost technology that enables long copper tubes, known as ‘straws’, to be coated on the inside with a thin layer of 10B-enriched boron carbide (10B4C).  Thermal neutrons captured in the 10B are converted into secondary particles, through the 10B(n, α) reaction.  The straws can be of various diameter (circa 4 mm to 15 mm), length (up to 2 m) and shape (round, star or pie) to increase the surface area of 10B.  Multiple straws can be packed inside a 1” diameter aluminium tube acting as a single drop-in replacement for traditional 3He detectors or individually distributed directly throughout the moderating medium, thus increasing efficiency by detecting the thermal neutrons at the point that they are created.  BCS-based detectors are widely used in systems for homeland security, safeguards and neutron imaging in direct exchange for 3He tubes.  This study aims to design a neutron monitor utilising BCS technology that is cheaper, more compact and produces comparable results to the existing network of NM-64 monitors.  Monte Carlo simulations using the MCNP radiation transport code to model several BCS-based solutions and an NM-64 computational benchmark are reported.  These models are validated experimentally using a standard PTI portal monitor (PTI-110-NDME) to determine its efficiency, dieaway, deadtime and gamma rejection using a combination of bare 252Cf, AmLi and 137Cs sources.  The PTI-110-NDME consists of a 12” x 5” x 1 m high density polyethylene (HDPE) slab with thirty ~15-mm diameter straws, 93 cm active length, embedded uniformly throughout the moderator.  Funded by UK Research & Innovation (UKRI), this research is part of the Space Weather Instrumentation, Measurement, Modelling and Risk (SWIMMR) programme.

How to cite: Aspinall, M., Binnersley, C., Bradnam, S., Croft, S., Joyce, M., Packer, L., and Wild, J.: Boron-coated straw detector technology as an alternative to helium-3 and boron trifluoride based proportional counters for ground level neutron monitoring: a design study., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5376, https://doi.org/10.5194/egusphere-egu22-5376, 2022.

EGU22-6352 | Presentations | ST1.6

Multiple interactions in a Neutron Monitor

Pierre-Simon Mangeard, John Clem, Paul Evenson, Waraporn Nuntiyakul, David Ruffolo, Alejandro Sáiz, Achara Seripienlert, and Surujhdeo Seunarine

The flux of low-energy (GeV-range) Galactic cosmic rays at Earth is modulated by the long term magnetic variations of the Sun (11-year sunspot cycle and 22-year magnetic solar cycle). This process known as Solar modulation is most pronounced at 1 GeV and below. However, it also operates at much higher energy, still exhibiting solar magnetic polarity dependence. For the last decades, ground-based neutron monitors provided valuable observations of the solar modulation up to a rigidity cutoff of about 17 GV. To extend the energy range of the neutron monitor observations, we recently upgraded the electronics of the Princess Sirindhorn Neutron Monitor in Thailand (PSNM, the operating neutron monitor at the highest geomagnetic rigidity cutoff) to record complex combinations of hits in multiple proportional counters. We present here the detection of multiple-hit events recorded at the PSNM. We discuss these observations with the help of a detailed Monte-Carlo simulation of energetic neutrons interacting in the detector. Finally, we estimate the nucleonic spectrum of the atmospheric secondary particles at the altitude of the detector.

How to cite: Mangeard, P.-S., Clem, J., Evenson, P., Nuntiyakul, W., Ruffolo, D., Sáiz, A., Seripienlert, A., and Seunarine, S.: Multiple interactions in a Neutron Monitor, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6352, https://doi.org/10.5194/egusphere-egu22-6352, 2022.

ST1.7 – Illuminating the Outer Heliosphere: ENA imaging from IBEX to IMAP

EGU22-3325 | Presentations | ST1.7

The Dispersive Nature of the Heliospheric Termination Shock

Bertalan Zieger, Joe Giacalone, Marc Swisdak, Gary Zank, and Merav Opher

The Voyager spacecraft are the first man-made objects to cross the termination shock (TS), where the solar wind becomes sub-fast magnetosonic due to the interaction with the local interstellar medium. Voyager 2 observations revealed that classical single-fluid magnetohydrodynamic (MHD) or multispecies single-fluid MHD models are not sufficient to describe the microstructure of the TS and the observed nonlinear waves downstream the TS. Consequently, more sophisticated physical models, like multifluid, hybrid or fully kinetic solar wind models, are needed to capture nonlinear waves, dispersive shock waves, and ion-ion instabilities, where each ion species (and electrons) can move independently with their own bulk velocities, and the fluctuating parts of the ion velocities are often comparable to the mean velocity of the collective plasma fluid. The multifluid simulation of the TS by Zieger et al. [2015] shows a remarkable agreement with high-resolution Voyager 2 observations, reproducing not only the microstructure of the third TS crossing (TS3) but also the energy partitioning among thermal ions, pickup ions (PUI), and electrons across the shock. It was demonstrated that TS3 is a subcritical dispersive shock wave with low fast magnetosonic Mach number and high plasma ß. Here we present multifluid, hybrid, and particle-in-cell (PIC) simulations of the second TS crossing (TS2) by Voyager 2, which was somewhat stronger than TS3, with an observed compression ratio of 2.2. All three types of simulations confirm the dispersive nature of the TS in agreement with Voyager 2 observations. We conclude that TS2, just as TS3, is a subcritical dispersive shock wave with a soliton (overshoot) at the leading edge of the shock and a quasi-stationary nonlinear wave train downstream of the shock front. We compared the cross-shock electric field in the multifluid, hybrid, and PIC simulations and found a reasonable agreement. We show that the Hall electric field is dominating over the convective and ambipolar electric fields, which indicates that electrons play an important role in the shock transition. Finally, we demonstrate that the microstructure of the termination shock is controlled by dispersion rather than ion reflection, and only slightly affected by reflected solar wind ions in the hybrid and PIC simulations, which validates the multifluid model on fluid scale. The dispersive nature of the termination shock has important implications for the transition and acceleration of PUIs across the termination shock, which is revealed in the PUI distributions in our hybrid [Giacalone et al., 2021] and PIC simulations.

How to cite: Zieger, B., Giacalone, J., Swisdak, M., Zank, G., and Opher, M.: The Dispersive Nature of the Heliospheric Termination Shock, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3325, https://doi.org/10.5194/egusphere-egu22-3325, 2022.

The heliosphere surrounding our solar system is formed by the interaction between the solar wind and the local interstellar medium as the Sun moves through interstellar space. With dimensions on the order of hundreds to potentially thousands of au, it is extremely difficult to pinpoint the 3D structure of the heliosphere and its boundaries, and the properties of the plasma within it. However, we can remotely measure the properties of the heliosphere with energetic neutral atoms (ENAs) which are created as a product of charge exchange between interstellar neutrals and ions within the solar wind plasma. ENAs can propagate hundreds of au before ionizing, allowing us to remotely view the distant boundaries of the heliosphere.

The Interstellar Boundary Explorer (IBEX) mission, a NASA smaller explorer mission which has been measuring ENA fluxes at ~0.5-6 keV for more than a solar cycle, has revealed at least two separate sources of ENAs: the “ribbon” of enhanced ENA fluxes forming a narrow, circular band across the sky, and the “globally distributed flux” (GDF) that forms lower intensity, broad features near the nose and tail of the heliosphere. While it is believed that the ribbon is formed from secondary ENAs from outside the heliopause, and ENAs from the inner heliosheath inside the heliopause are a major contributor to the GDF, it is not clear exactly how much of the GDF may originate outside the heliopause, and how much of the flux observed in the Ribbon is from the GDF itself. To help solve this issue, we present recent developments in our understanding of the ribbon vs. GDF sources from both IBEX data analysis and modeling perspectives. Moreover, with the upcoming IMAP mission set to launch in 2025, we provide insight into how IMAP’s enhanced capabilities may improve our current understanding of the heliosphere.

How to cite: Zirnstein, E.: Differentiating the Ribbon and Globally Distributed ENA Flux in IBEX Observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13186, https://doi.org/10.5194/egusphere-egu22-13186, 2022.

Space plasmas reside in non-equilibrium stationary states described by kappa distributions. The high-energy asymptotic behavior of kappa distributions leads to a power-law relationship of the energy-flux spectra; this relationship, when observed, can be analyzed for determining the thermodynamic parameters of the plasma. In the presented analysis, we use Energetic Neutral Atom (ENA) observations from the IBEX-Hi sensor, converted to the corresponding proton plasma spectra of the inner heliosheath, and timestamped with the ENA creation time. We, then, model the proton spectra with kappa distributions and derive the sky maps of the (radially averaged) values of temperature, density, kappa, and other thermodynamic parameters of the proton plasma in the inner heliosheath. We examine the variations of the determined thermodynamics and whether a correlation exists with solar activity during the 24th solar cycle.

How to cite: Livadiotis, G.: Thermodynamics of the proton plasma in the inner heliosheath during the 24th solar cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13574, https://doi.org/10.5194/egusphere-egu22-13574, 2022.

The Voyager 1 and Voyager 2 (V1 & V2) crossings of the termination shock (TS; ~94 and ~84 AU, respectively), led to the first measurements of ions and electrons that constitute the heliosheath (HS). Their crossings of the heliopause (HP; ~122 AU and ~119 AU), pinpointed the extent of the upwind heliosphere's expansion into the Very Local Interstellar medium (VLISM). The Cassini/INCA >5.2 keV ENA images of the celestial sphere, have placed the local V1&2/LECP measurements in a global context and have led to the discovery of a high intensity and wide ENA region that encircles the celestial sphere, called “Belt” and corresponds to a “reservoir” of particles that exist within the HS. The heliosphere forms a time-dependent, roughly symmetric obstacle to the inward interstellar flow, responding within ~2-3 yrs, in both the nose and anti-nose directions to the outward propagating solar wind changes through the solar cycle. The shape of the ion energy spectra plays a critical role in determining the pressure balance and acceleration mechanisms inside the HS. Energy spectra from ~10 eV to 344 MeV show that the PUIs dominate the total pressure distribution inside the HS, but suprathermal ions provide a significant contribution that cannot be neglected, revealing that >5.2 keV ENAs serve as important indicators of the acceleration processes that the parent H+ population undergoes inside the HS, thus imposing a key constraint on any future interpretation concerning the HS dynamics. The combination of ENAs and ions in the HS show that the plasma beta is >>1, the magnetic field upstream at the heliopause required to balance the pressure from the HS is >0.5 nT (V1 direction) and ~0.67 nT (V2 direction) and that the neutral Hydrogen density is ~0.12/cm3. These inferred values are consistent with measurements from both V1 and V2 spacecraft. Energetic ion measurements from V1/LECP in and beyond the HP show an average radial inflow of 40-139 keV ions for ~10 AU inside the HS and an average radial outflow over a spatial range of ~28 AU past the HP. These particles correspond to an ion population leaking from the HS into interstellar space, most likely due to the flux tube interchange instability at the boundary and provide a direct observation of the communication between the HS and the VLISM. They may also provide an important constraint for future models that aim to explain the <6 keV ENA ribbon fluxes (measured from the IBEX mission), which are likely formed from the neutralization of energetic pickup ions gyrating in the IS magnetic field outside the HP, reflecting (in part) those ion distributions that are responsible for the formation of this unexpected structure.

How to cite: Dialynas, K., Krimigis, S., Decker, R., and Hill, M.: Highlights of the combination of “Ground truth” >28 keV in-situ ions from the Voyagers and >5.2 keV ENAs from Cassini in the study of the global heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4316, https://doi.org/10.5194/egusphere-egu22-4316, 2022.

EGU22-1608 | Presentations | ST1.7

High-frequency waves driven by pickup ion ring-beam distributions in the outer heliosheath

Kaijun Liu, Ameneh Mousavi, and Sina Sadeghzadeh

Scattering of pickup ion ring-beam distributions in the outer heliosheath is a fundamental element in the spatial retention scenario of the energetic neutral atom (ENA) ribbon observed by the Interstellar Boundary EXplorer (IBEX). According to our earlier linear instability analysis, pickup ion ring-beam distributions trigger magnetic field-aligned, right-hand polarized unstable waves in two separate frequency ranges which are near and far above the proton cyclotron frequency, respectively. We have performed hybrid simulations to study the unstable waves near the proton cyclotron frequency. However, the high-frequency waves well above the proton cyclotron frequency are beyond the reach of hybrid simulations. In the present study, particle-in-cell simulations are carried out to investigate the parallel- and anti-parallel-propagating high-frequency waves excited by the outer heliosheath pickup ions at different pickup angles as well as the scattering of the pickup ions by the waves excited. In the early stages of the simulations, the results confirm the excitation of the parallel-propagating, right-hand polarized high-frequency waves as predicted by the earlier linear analysis. Later in the simulations, enhanced anti-parallel-propagating modes also emerge. Furthermore, the evolution of the pickup ion ring-beam distributions of the selected pickup angles reveals that the high-frequency waves do not significantly contribute to the pickup ion scattering. These results are favorable regarding the plausibility of the spatial retention scenario of the IBEX ENA ribbon.

How to cite: Liu, K., Mousavi, A., and Sadeghzadeh, S.: High-frequency waves driven by pickup ion ring-beam distributions in the outer heliosheath, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1608, https://doi.org/10.5194/egusphere-egu22-1608, 2022.

EGU22-11016 | Presentations | ST1.7

Recent results from neutral beam source calibration by means of the novel Absolute Beam Monitor

Jonathan Gasser, André Galli, and Peter Wurz

The IMAP mission by NASA is dedicated to extending the physical understanding of our heliosphere and its interaction with the interstellar medium by enhancing and refining the results obtained from IBEX. The neutral atom analysis instrument IMAP-Lo will observe and map fluxes of low-energy heliospheric neutral atoms (ENAs) and interstellar neutral (ISN) H, D, He, O and Ne with energies as low as 10 eV up to 1000 eV.

The instrument testing and calibration with a neutral atom beam is foreseen in the MEFISTO test facility for ion and neutral particle instruments at the University of Bern. MEFISTO is equipped with an electron-cyclotron resonance ion source that provides ion beams at a beam energy 3keV/q up to 100 keV/q. The beam fed into the test chamber is decelerated to 10 eV/q – 3 keV/q and effectively neutralized in a removable neutralization stage via surface reflection on a highly polished single crystal tungsten surface. The relative neutral beam intensity is permanently monitored via the neutralizing surface current. The neutralization process induces a considerable reduction of particle kinetic energy and conical widening of the neutral beam.

Thus, one key improvement for the calibration of a neutral atom instrument such as IMAP-Lo is to be able to measure the absolute neutral particle flux and beam energy into the instrument in the test chamber. To achieve this goal, the Absolute Beam Monitor (ABM) was developed recently.

The ABM is a dedicated laboratory device for absolute neutral particle flux measurements below 3 keV and coarse kinetic energy determination. Neutrals entering the ABM aperture strike a single crystal W conversion surface at grazing angle and are reflected into a channeltron to generate a stop pulse. The simultaneous monitoring of secondary electrons released at the W surface as start signal, the stop signal and the coincidence event rate allows inferring the rate of neutral atoms into the ABM aperture. The average neutral beam energy is obtained from the start-stop time-of-flight spectrum. The ABM is the first and so far the only device to measure the absolute neutral atoms flux in this low energy range below a few 100 eV. It serves as a primary standard for gauging the MEFISTO neutral beam source.

We report on recent calibration results of neutral H, He, O, Ne beams in the 10 eV – 1 keV energy range with the ABM in MEFISTO.

How to cite: Gasser, J., Galli, A., and Wurz, P.: Recent results from neutral beam source calibration by means of the novel Absolute Beam Monitor, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11016, https://doi.org/10.5194/egusphere-egu22-11016, 2022.

As the Sun moves through its local galactic neighborhood, it disturbs the ionized component of interstellar matter, forming a complex bow-wave structure of a slowed and heated, magnetized plasma, flowing past the heliosphere. This region is called the outer heliosheath. The neutral component of interstellar matter is in equilibrium with the ionized component far ahead of the heliosphere, but within the outer heliosheath it decouples kinematically from the perturbed plasma. A complex interaction begins, mostly by charge exchange, between the ions and the neutral atoms, and as a result, a new population of neutral atoms is created, with kinematic parameters similar to that of the surrounding plasma. In addition, elastic collisions operate, additionally modifying both the original primary and the secondary population of neutral. Both the primary and the secondary populations penetrate inside the heliosphere and can be directly sampled at 1 au. We will review results of observations of these populations obtained from IBEX-Lo and results of modeling of the secondary populations of interstellar hydrogen, helium, and oxygen in the outer heliosheath. We will illustrate how these populations can be better observed owing to enhanced capabilities of the planned IMAP-Lo instrument and demonstrate how they can be leveraged to resolve the primary and secondary populations, and investigate the properties of local interstellar matter in the immediate neighborhood of the Sun.

How to cite: Bzowski, M.: The primary and secondary populations of interstellar neutral gas as seen now by IBEX and in the future by IMAP, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13535, https://doi.org/10.5194/egusphere-egu22-13535, 2022.

EGU22-6402 | Presentations | ST1.7

Interstellar Neutral He Parameters from Crossing Parameter Tubes with the Interstellar Mapping and Acceleration Probe (IMAP) informed by 10 Years of Interstellar Boundary Explorer (IBEX) Observations

Nathan Schwadron, Eberhard Moebius, David McComas, Jon Bower, Maciek Bzowski, Stephen Fuselier, David Heirtzler, Marzena Kubiak, Marty Lee, Fatemeh Rahmanifard, Justyna Sokol, Pawel Swaczyna, and Reka Winslow

The Sun’s motion relative to the surrounding interstellar medium leads to an interstellar neutral (ISN) wind through the heliosphere. For several species, including He, this wind is moderately depleted by ionization and can be analyzed in-situ with pickup ions and direct neutral atom imaging.  Since 2009, observations of the wind at 1 AU with the Interstellar Boundary Explorer (IBEX) have returned a precise 4-dimensional parameter tube for the flow vector (speed VISN, longitude λISN, and latitude βISN) and temperature TISN of interstellar He in the local cloud, which organizes VISN, λISN, and TISN as a function of λISN, and the local flow Mach number (Vth−ISN/VISN).  We refer to this functional dependence as the 4D IBEX parameter tube. On IBEX, the limitation of measuring the ISN flow observations to nearly perpendicular to the Earth-Sun line limits the range of observations in ecliptic longitude to ∼ 30º.  This limitation results in large uncertainties along the IBEX parameter tube and relatively small uncertainties across the parameter tube.   Over the past three years, IBEX operations were modified to let the spin axis pointing of IBEX drift to the maximum offset (7º) west of the Sun, which is the limit for the IBEX spacecraft. This expansion of the IBEX viewing helps break the degeneracy of the ISN parameters along the 4D IBEX parameter tube. It complements the full χ-square-minimization to obtain the ISNs parameters through comparison with detailed models of the ISN flow. The next generation IBEX-Lo sensor on IMAP will be mounted on a pivot platform, enabling IMAP-Lo to follow the ISN flow over almost the entire spacecraft orbit around the Sun.  A near-continuous set of 4D parameter tubes on IMAP will be observed for He, and for O, Ne, and H that cross at varying angles in the full ISN parameter space. This analysis substantially reduces the flow parameter uncertainties for these species and mitigating systematic uncertainties, such as those from ionization effects and the presence of secondary components. We discuss implications of these measurements for understanding our environment and its relationship to the structure of the local interstellar medium. Thus, we discuss how IMAP will probe the interstellar neutral gas flow in detail to derive the precise parameters of the interstellar flow and relate these conditions to understand our place within the interstellar medium. 

How to cite: Schwadron, N., Moebius, E., McComas, D., Bower, J., Bzowski, M., Fuselier, S., Heirtzler, D., Kubiak, M., Lee, M., Rahmanifard, F., Sokol, J., Swaczyna, P., and Winslow, R.: Interstellar Neutral He Parameters from Crossing Parameter Tubes with the Interstellar Mapping and Acceleration Probe (IMAP) informed by 10 Years of Interstellar Boundary Explorer (IBEX) Observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6402, https://doi.org/10.5194/egusphere-egu22-6402, 2022.

EGU22-6502 | Presentations | ST1.7

Filtration and Scattering of Interstellar Neutral Helium beyond the Heliopause

Paweł Swaczyna, Maciej Bzowski, Stephen Fuselier, André Galli, Jacob Heerikhuisen, Marzena Kubiak, David McComas, Eberhard Möbius, Fatemeh Rahmanifard, Nathan Schwadron, and Eric Zirnstein

The pristine very local interstellar medium (VLISM) is not available for in situ observations even with the Voyager spacecraft because the influence of the heliosphere on the VLISM plasma extends up to several hundred au from the Sun. Therefore, observations of interstellar neutral (ISN) helium, the species least modified at the heliospheric boundaries, are used to determine the pristine VLISM flow speed, direction, and temperature. For more than one solar cycle, the Interstellar Boundary Explorer (IBEX) has sampled ISN helium atoms at 1 au, significantly reducing the statistical uncertainties of the ISN helium flow parameters. Launching in 2025, the Interstellar Mapping and Acceleration Probe (IMAP) will further lower these uncertainties thanks to the utilization of a pivot platform, which provides a range of viewing orientations and reduces the parameter degeneracy seen from IBEX data. Even though interstellar helium is the least modified ISN species, recent studies show that the ISN helium flux is affected by charge exchange and elastic collisions beyond the heliopause. Charge exchange collisions outside the heliopause filter the primary ISN helium and produce a secondary population from perturbed He+ ions in the interstellar plasma. The secondary helium population, originally called the Warm Breeze, was discovered from IBEX observations. Moreover, the distribution function of the primary ISN helium population is modified by elastic collisions with slowed down and heated plasma ahead of the heliopause. Consequently, the combined primary and secondary ISN helium populations at 1 au are complex and cannot be separated. Furthermore, the modifications of the population properties are larger than the statistical uncertainty of IBEX observations. We use global heliosphere models to estimate the magnitude of the filtration and scattering caused by charge exchange and elastic collisions. Together with other sources of information about the VLISM, these estimates allow us to assess the pristine VLISM conditions outside of heliosphere influences. 

How to cite: Swaczyna, P., Bzowski, M., Fuselier, S., Galli, A., Heerikhuisen, J., Kubiak, M., McComas, D., Möbius, E., Rahmanifard, F., Schwadron, N., and Zirnstein, E.: Filtration and Scattering of Interstellar Neutral Helium beyond the Heliopause, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6502, https://doi.org/10.5194/egusphere-egu22-6502, 2022.

EGU22-13568 | Presentations | ST1.7

Pressure Balance at the Heliosphere Boundary and in the Local Interstellar Cloud

Eberhard Möbius and Jeffey Linsky

The pressures exerted by the solar wind from the inside and the interstellar medium from the outside control the size and shape of the heliosphere. Magnetic fields and cosmic rays play important roles to varying extents on both sides. We will assess the pressure balance by assembling the relevant component pressures in the (inner) heliosheath inside the heliopause, in the Very Local Interstellar Medium (VLISM, interstellar medium affected by the presence of the heliosphere or outer heliosheath), and in the Local Interstellar Cloud (LIC) unaffected by the heliosphere. We take the cosmic ray pressure from Voyager observations, which don’t show substantial gradients beyond the heliopause. The remaining pressure on the heliopause from inside is due to thermal and suprathermal ions in the subsonic solar wind, obtained from IBEX and INCA ENA observations and Voyager in situ measurements at the higher energies.

Besides cosmic rays, the pressure in the undisturbed LIC is composed of magnetic field pressure taken from IBEX Ribbon observations and related modeling. Thermal and turbulent pressures are based on H and He neutral and ion densities from pickup ion and interstellar gas flow observations, combined with the temperature and turbulent speed from absorption-line observations. The total LIC pressure in its rest frame is almost 40% lower than the pressure inside the heliopause, whereas adding the full ram pressure based on the LIC velocity relative to the Sun exceeds that pressure substantially. We estimate the likely effective pressure on the heliopause by combining the compressed interstellar magnetic field, as measured by Voyager, and the compressed and heated interstellar plasma, resorting to results from global heliospheric modeling. An interesting result of these pressure comparisons is that the effective ram pressure on the heliopause is somewhat larger than the combined magnetic field, thermal, and turbulent pressure in the LIC, which points to the importance of the LIC ram pressure for the shape of the heliosphere. We also compare the LIC pressure with the gravitational pressure on the galactic disk at the location of the Sun.

How to cite: Möbius, E. and Linsky, J.: Pressure Balance at the Heliosphere Boundary and in the Local Interstellar Cloud, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13568, https://doi.org/10.5194/egusphere-egu22-13568, 2022.

ST1.8 – Open Session on the Sun and Heliosphere

EGU22-939 | Presentations | ST1.8

Covariation of solar granulation size and sunspot indices in activity cycle 24

Alexey Sharov and Arnold Hanslmeier

New theoretical arguments and empirical evidence for correlated changes in sun granulation size and sunspot indices were obtained during this two-year study using blue continuum image data acquired by the Hinode solar optical telescope in 2006-2016 and simultaneous time series of daily sunspot numbers (SSN) and areas (SSA). An original set of simple scaling equations linking the relative variation in the average size of granular cells to the sum change in the total number of granular cells, SSA and surface gravity was written under the assumption that at the height of the blue continuum formation, the entire surface of the Sun is the sum of the areas of granular cells, pores and sunspots. The magnitudes of relative changes in the horizontal size of granular cells due to variations in global solar parameters were estimated and it was shown that variations in the SSA have the dominant influence on variations in the mean granular size. Periodic spurious changes in the mean granular size due to the sun's variable tilt with respect to the telescope and apparent changes in rotational speed and surface gravity were also mentioned.

Our empirical research focussed on the automatic identification and precise morphometric measurements of granular cells in high-resolution Hinode images using an efficient marker-controlled watershed segmentation algorithm. A total of seven image sequences with a 30-, 27- and 1-day cadence, all of which contained 840 images, were compiled, processed and corrected with regard to the variable sun-earth distance and heliographic coordinates. The resultant granulation parameters, including mean area, equivalent diameter, extent and contrast were compared to SSN and SSA data using temporal cross-correlation. An essential anti-correlation was measured between the mean size of granular cells and the daily SSN for the medium time intervals of four months, which were characterized with the optimal orbital conditions for the imaging of solar granulation. The decrease in the cellular scale by 3% with the increase in the average SSN index of 20%, was revealed for both ascending and descending phases of the 24th activity cycle, while the average contrast characterizing image quality remained almost unchanged. The approximately 14-day delay in the cause-effect relationship between the SSN and the granulation scale was revealed and a plausible explanation for this delay was given.

In the quiet sun at the disk centre, the mean equivalent diameter of granules was measured at 1.37 arcseconds, while the same parameter for granular cells was given as 2.06 arc seconds, which was in good agreement with the results of other researchers. In the close vicinity of sunspots, the mean size of granular cells decreased by a few percent, while the width of intergranular lanes decreased by 60%, indicating the existence of bright rings with higher temperatures around these sunspots. The significance of all these observations is that they confirm the results of the predecessors, positively support the 70-year-old hypothesis about the dependence of granulation properties on the sunspot cycle, and stimulate the use of the granulation scale as a cyclical proxy for solar activity over medium-term periods.

How to cite: Sharov, A. and Hanslmeier, A.: Covariation of solar granulation size and sunspot indices in activity cycle 24, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-939, https://doi.org/10.5194/egusphere-egu22-939, 2022.

EGU22-9622 | Presentations | ST1.8

Clarifying the relation between chromospheric emissions and photospheric magnetic fields using AIA 1600 Å and HMI data

Ismo Tähtinen, Ilpo Virtanen, Alexei Pevtsov, and Kalevi Mursula

Intense photospheric magnetic fields manifest as enhanced emission in several spectral lines and parts of the continuum. Here we aim to improve the understanding of the relation between magnetic fields and radiative structures by using the seeing-free observations of the Atmospheric Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI), both on-board Solar Dynamics Observatory (SDO). We use AIA 1600 Å band, which captures the far-ultraviolet continuum emission originating from the temperature minimum of the solar chromosphere.

We developed a novel, objective method to define thresholds separating the brightest AIA 1600 Å pixels ("bright pixels") and the least bright pixels ("dark pixels") from the AIA 1600 Å brightness distribution. According to the method bright pixels are pixels whose standardized contrast (ratio of brightness to the center-to-limb variation) exceeds the level of I = 1.93. This threshold maximizes the average size of bright clusters (4-connected regions of bright pixels). Dark pixels are pixels whose standardized contrast is below I = 0.5. This corresponds to a threshold below which there are practically no pixels on quiet days. Comparing the AIA 1600 Å intensity and HMI magnetic field observations, we found that the AIA 1600 Å dark pixels correspond to the strongest magnetic field (B > 1325 G) pixels. These pixels are typically within sunspots. On the other hand, we found the AIA bright pixels correspond to moderate (55 G < B < 475 G) magnetic field intensity pixels of HMI.

We found that the percentage of AIA bright pixels on the solar surface almost entirely explains the observed variability of the total AIA 1600 Å emission, even in the presence of large sunspot groups. We developed a multi-linear regression model, which reliably predicts the magnitude of the disk-averaged unsigned magnetic field using the measured percentages of bright and dark pixels. We found that the large bright clusters have a constant mean unsigned magnetic field, similarly as earlier found for, e.g., Ca II K plages. However, the magnetic field strength of bright clusters is 246.5 ± 0.1 G, which is roughly 100 G larger than found earlier for Ca II K plages.

How to cite: Tähtinen, I., Virtanen, I., Pevtsov, A., and Mursula, K.: Clarifying the relation between chromospheric emissions and photospheric magnetic fields using AIA 1600 Å and HMI data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9622, https://doi.org/10.5194/egusphere-egu22-9622, 2022.

EGU22-4178 | Presentations | ST1.8

Predicting the solar cycle amplitude with the new catalogue of hemispheric sunspot numbers

Shantanu Jain, Tatiana Podladchikova, Astrid M. Veronig, Olga Sutyrina, Mateja Dumbović, Frédéric Clette, and Werner Pötzi

The sun’s magnetic field drives the 11-year solar cycle, and predicting its strength has practical importance for many space weather applications. Previous studies have shown that analysing the solar activity of the two hemispheres separately instead of the full sun can provide more detailed information on the activity evolution. However, the existing Hemispheric Sunspot Number data series (1945 onwards) was too short for meaningful solar cycle predictions. Based on a newly created hemispheric sunspot number catalogue for the time range 1874-2020 (Veronig et al. 2021, http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/652/A56) that is compatible with the International Sunspot Number from World Data Centre SILSO, we investigate the evolution of the solar cycle for the two hemispheres and develop a novel method for predicting the solar cycle amplitude. We demonstrate a steady relationship between the maximal growth rate of activity in the ascending phase of a cycle and its subsequent amplitude and form a 3rd order regression for the predictions. Testing this method for cycles 12-24, we show that the forecast made by the sum of the maximal growth rate from the North and South Hemispheric Sunspot number is more accurate than the same forecast from the Total Sunspot Number: The rms error of predictions is smaller by 27%, the correlation coefficient r is higher by 11% on average reaching values in the range r = 0.8-0.9 depending of the smoothing window of the monthly mean data. These findings demonstrate that empirical solar cycle prediction methods can be enhanced by investigating the solar cycle dynamics in terms of the hemispheric sunspot numbers, which is a strong argument supporting regular monitoring, recording, and analysing solar activity separately for the two hemispheres.

How to cite: Jain, S., Podladchikova, T., Veronig, A. M., Sutyrina, O., Dumbović, M., Clette, F., and Pötzi, W.: Predicting the solar cycle amplitude with the new catalogue of hemispheric sunspot numbers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4178, https://doi.org/10.5194/egusphere-egu22-4178, 2022.

With current observational methods it is not possible to determine the magnetic field in the solar corona accurately. Therefore, coronal magnetic field models have to rely on extrapolation methods using photospheric magnetograms as boundary conditions. In recent years, due to the increased resolution of observations and the need to resolve non-force-free lower regions of the solar atmosphere, there have been increased efforts to use magnetohydrostatic (MHS) field models instead of force-free extrapolation methods. Although numerical methods to calculate MHS solutions can deal with non-linear problems and hence provide more accurate models, analytical three-dimensional MHS equilibria can also be used as a numerically relatively “cheap” complementary method.

 

We discuss a family of analytical MHS equilibria that allows for a transition from a non-force-free region to a force-free region. The solution involves hypergeometric functions and while routines for the calculation of these are available, this can affect both the speed and the numerical accuracy of the calculations. We therefore look into the asymptotic behaviour of this solution in order to numerically approximate it through exponential functions aiming to improve the numerical efficiency. We present an illustrative example by comparing field line profiles, density and pressure differences between the exact solutions, the asymptotic solution and a hybrid model where the use of the hypergeometric function is restricted to an area around the transitional region between the non-force-free and the force-free domain.

How to cite: Nadol, L. and Neukirch, T.: Coronal Magnetic Field Extrapolation Using a Specific Family of Analytical 3D Magnetohydrostatic Equilibria — Practical Aspects, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9430, https://doi.org/10.5194/egusphere-egu22-9430, 2022.

EGU22-7840 | Presentations | ST1.8

The exoplanetary magnetosphere extension in Sun-like stars based on the solar wind and solar UV emission

Raffaele Reda, Luca Giovannelli, Tommaso Alberti, Francesco Berrilli, Luca Bertello, Dario Del Moro, Maria Pia Di Mauro, Piermarco Giobbi, and Valentina Penza

The solar activity in form of coronal mass ejections or solar wind disturbances, such as slow or high speed streams, affects the circumterrestrial electromagnetic environment, with a primary effect on the magnetosphere, compressing and perturbing it. Here, in order to connect the long-term solar activity variations to solar wind properties, we use measurement of a proxy for chromospheric activity, the Ca II K index, and solar wind OMNI data for the time interval 1965-2021, which almost entirely covers the last 5 solar cycles. By using both a cross correlation and a mutual information approach, a 3.6-year mean lag has been found between Ca II K index and solar wind dynamic pressure. This result allows us to obtain a relationship between the solar UV emission and the solar wind dynamic pressure, enabling us to derive the Earth’s magnetospheric extension over the last 5 solar cycles.
Moreover, the advantage of having used the Ca II K index proxy is that the relation found for the Sun can be easily extended to other stars with similar properties (i.e. Sun-like stars). To this scope, the model is then used to study the effect of stellar wind dynamic pressure on the magnetosphere of Earth-like planets orbiting at 1 AU around a sample of Sun-like stars.

How to cite: Reda, R., Giovannelli, L., Alberti, T., Berrilli, F., Bertello, L., Del Moro, D., Di Mauro, M. P., Giobbi, P., and Penza, V.: The exoplanetary magnetosphere extension in Sun-like stars based on the solar wind and solar UV emission, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7840, https://doi.org/10.5194/egusphere-egu22-7840, 2022.

EGU22-12590 | Presentations | ST1.8

How to identify important magnetic helicity locations in solar active regions

Kostas Moraitis, Spiros Patsourakos, and Alexander Nindos

Magnetic helicity is a physical quantity of great importance in the study of magnetized plasmas as it is conserved in ideal magneto-hydrodynamics and slowly deteriorating in non-ideal conditions such as magnetic reconnection. A meaningful way of defining a density for helicity is with field line helicity, which, in solar conditions, is expressed by relative field line helicity (RFLH). Here, we study in detail the behaviour of RFLH in the large, well-studied, eruptive solar active region (AR) 11158. The computation of RFLH and of all other quantities of interest is based on a high-quality non-linear force-free reconstruction of the AR coronal magnetic field, and on the recent developments in its computational methodology. The derived photospheric morphology of RFLH is very different than that of the magnetic field or the electrical current, and also manages to depict the large decrease in the value of helicity during an X-class flare of the AR. Moreover, the area of the RFLH decrease coincides with the location of the magnetic structure that later erupted, the flux rope. Based on these results we review the necessary steps one needs to follow in order to identify the locations in an AR where magnetic helicity is more important. This task can provide crucial information for the conditions of an AR, especially during eruptive events.

How to cite: Moraitis, K., Patsourakos, S., and Nindos, A.: How to identify important magnetic helicity locations in solar active regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12590, https://doi.org/10.5194/egusphere-egu22-12590, 2022.

EGU22-564 | Presentations | ST1.8

Study on the association of solar gyroresonance emission sources with brightness temperature intensification at 17 GHz

Abimael Amaro, Marlos Rockenbach da Silva, and Joaquim Eduardo Rezende Costa

Remarkable works done in the last decades by many authors on the solar gyroresonance mechanism have illuminated the way to establish the relationship between this form of emission and magnetic fields in the solar atmosphere and to know the magnetic nature of the middle and upper layers of the active regions. Despite all these advances, solar physics still needs a direct means (without magnetograms) of identifying the sources of gyroresonance emission.
In search of a solution to this problem, we used solar images at 17 GHz synthesized by the Nobeyama Radioheliograph (NoRH) to map the likely sources of gyroresonance. 
To achieve this result, we first hypothesized that gyroresonance and bremsstrahlung mechanisms can generate a large brightness temperature intensification due to the close relationship such mechanisms have with magnetic fields and because of the role of the magnetic field in controlling the brightness of the solar atmosphere in the radiofrequency range.
To test this hypothesis regarding the gyroresonance process, we selected 8 large active regions (ARs) among the HMI magnetograms generated by the Solar Dynamics Observatory (SDO) corresponding to the 1st half of the 24th solar cycle.  We then analyzed each AR through its magnetogram and its image at 17 GHz. Aiming to verify, in these radio maps, whether there is a correspondence between brightness bumps and parameters associated with gyroresonance emission, we constructed three categories of brightness maps for each active region, respectively presenting the field of: brightness temperature in BT maps, brightness temperature gradient in BTG maps, and brightness temperature gradient to brightness temperature ratio in BTG/BT maps. Such parameters are the characteristic circular polarization, whose modulus is greater than 30%, and characteristic magnetic field strengths, associated with the gyroresonance radiation at 17 GHz for 3rd and 4th harmonics. Such a step also aimed to verify which of these categories would best map the putative sources of gyroresonance emission.
On these maps, we then plotted the contours of the characteristic parameters. 
For each AR, we also obtained the degree of correlation between its brightness variables and the characteristic polarization. We then observed that the contours of characteristic magnetic field strengths are predominantly enveloped by the area of the brightness bumps, while the contours of the characteristic polarization fit well to such areas, being better fitted to the relative bumps (in the BTG/BT maps). In the statistical analysis, we observe that for each active region, there is a predominance of strong correlations between the brightness variables and the modulus of the characteristic polarization. Such correlation tends to be highest for the brightness temperature. For each brightness variable, the highest correlations tend to occur for the predominant polarization direction of the active region.
The data, therefore, indicate a high probability that the gyroresonance emission mechanism was at least one of the important causes of the radio bumps produced in the observed active regions.

How to cite: Amaro, A., Rockenbach da Silva, M., and Rezende Costa, J. E.: Study on the association of solar gyroresonance emission sources with brightness temperature intensification at 17 GHz, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-564, https://doi.org/10.5194/egusphere-egu22-564, 2022.

EGU22-1710 | Presentations | ST1.8

Evolution of alpha particle content at flux rope boundaries as seen by Solar Orbiter

Lubomir Prech, Tereza Durovcova, Jana Safrankova, Zdenek Nemecek, Philippe Louarn, and Andrey Fedorov

Prominences and filaments are manifestations of magnetised, levitated plasma within the solar coronal atmosphere. Expanding on our previous 2.5D work presented in Jenkins & Keppens (2021), we will present a state-of-the-art magnetohydrodynamic simulation that yields the first fully 3D model to successfully unite the extreme-ultraviolet and Hydrogen-α prominence views that contain radial striations with the equivalent on-disk filaments comprised of finite width threads. Owed to the unprecedented resolution with which this simulation is carried out, we complete a full observational synthesis and provide predictions of exactly what the instruments associated with the upcoming Solar Orbiter and DKIST will observe. We then begin with an analysis of all hydromagnetic sources of the vorticity evolution and find the internal plasma dynamics to be consistent with the nonlinear development of the magnetic Rayleigh-Taylor instability. A further stability analysis that drops the strict, idealised mRTi initial conditions then enables us to tentatively characterise the preceding linear development as the general (quasi-) interchange gravitational instability. Our simulations and analyses show clearly how this universal interchange process operates, and how our results and conclusions finally unify the contradictory prominence/filament perspectives.

How to cite: Jenkins, J. and Keppens, R.: The Role of the Magnetic Rayleigh-Taylor Instability in Resolving the Solar Prominence/Filament Paradox, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2438, https://doi.org/10.5194/egusphere-egu22-2438, 2022.

EGU22-5443 | Presentations | ST1.8

Large Amplitude Oscillations in Solar Filaments Caused by Solar Jets

Reetika Joshi, Manuel Luna, Brigitte Schmieder, Fernando Moreno-Insertis, and Ramesh Chandra

Large amplitude oscillations (LAO) are often detected in filaments. Their origin has been associated with shock waves or to interaction with eruptions and jets. In this study we present  two examples of LAOs due to solar jets interaction with filaments on February 3-5 2015 and March 14 2015.  The filament eruption on March 14 was followed by a two step filament eruption along with a CME and become the strong geomagnetic storm of Solar Cycle 24 on 17 March 2015. These LAOs are  analysed by using time-distance diagnostics. The detected LAOs have periods of around 60 minutes and are damped after three oscillations. The observations are consistent with the results of a recent developed theoretical model of jet and filament interaction. The jets are associated with very weak flares which did not initiate any EUV wave. The role of waves as trigger of these oscillations can be discarded for these two events. 

 

How to cite: Joshi, R., Luna, M., Schmieder, B., Moreno-Insertis, F., and Chandra, R.: Large Amplitude Oscillations in Solar Filaments Caused by Solar Jets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5443, https://doi.org/10.5194/egusphere-egu22-5443, 2022.

EGU22-13141 | Presentations | ST1.8

MHD avalanches in truly curved coronal arcades: proliferation and heating

Jack Reid, James Threlfall, and Alan W. Hood

MHD avalanches involve small, narrowly localized instabilities spreading across neighbouring areas in a magnetic field. Cumulatively, many small events release vast amounts of stored energy. Straight cylindrical flux tubes are easily modelled, between two parallel planes, and can support such an avalanche: one unstable flux tube causes instability to proliferate, via magnetic reconnection, and then an ongoing chain of like events. True coronal loops, however, are visibly curved, between footpoints on the same solar surface. With 3D MHD simulations, we verify the viability of MHD avalanches in a more physical, curved geometry, in a coronal arcade. MHD avalanches thus amplify instability across strong astrophysical magnetic fields and disturb wide regions of plasma. Contrasting with the behaviour of straight cylindrical models, a modified ideal MHD kink mode occurs, more readily and preferentially upwards. Instability spreads over a region far wider than the original flux tubes and their footpoints. Consequently, sustained heating is produced in a series of 'nanoflares', collectively contributing substantially to coronal heating. Overwhelmingly, viscous heating dominates, generated in shocks and jets produced by individual small events. Reconnection is not the greatest contributor to heating, but rather facilitates those processes that are. Localized and impulsive, heating shows no strong spatial preference, except a modest bias away from footpoints, towards the loop's apex.

How to cite: Reid, J., Threlfall, J., and Hood, A. W.: MHD avalanches in truly curved coronal arcades: proliferation and heating, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13141, https://doi.org/10.5194/egusphere-egu22-13141, 2022.

EGU22-11326 | Presentations | ST1.8

Dynamics of helium abundance inside and around ICME

Alexander Khokhlachev, Yuri Yermolaev, Maria Riazantseva, Liudmila Rakhmanova, and Irina Lodkina

The interplanetary manifestations of coronal mass ejections (ICME) typically characterized by an increased relative abundance of doubly ionized helium, which can be several time higher comparative to the slow solar wind streams and exceed 10%. At the same time the helium abundance can dynamically change as a result of local processes in solar wind plasma. However, the details of helium abundance dynamic have not yet been sufficiently studied.

The study is devoted to the changing of the helium abundance inside the ICME including both its types - Magnetic Clouds (MC) and EJECTA, and also in the vicinity of these large scale structures. We consider the helium abundance dynamic, and its relation with other solar wind parameters both at large (>106 km) and medium (104-105 km) scales, based on the statistic and correlation analysis of plasma and magnetic field parameters [Yermolaev et al., 2020; Khokhlachev et al., 2021]. Hourly average data from OMNI-2 database and 3 second WIND spacecraft measurements are used for the analysis of corresponding scales. Selection of the intervals related to ICME events (MC, EJECTA and SHEATH regions) was produced with the help of the catalog of large-scale events of Space Research Institute (http://iki.rssi.ru/pub/omni/catalog/ [Yermolaev et al., 2009]). It is shown that on large scales the helium abundance generally increases with a decrease in the plasma parameter β in the ICME. This relation can be predominantly explained by the strong positive correlation of helium abundance with magnetic pressure, while correlation with thermal pressure is ambiguous: weak negative for Magnetic Clouds and weak positive for EJECTA. This confirms the previously proposed hypothesis of the ion current flow enriched by helium ions inside the ICME [Yermolaev et al., 2020]. On medium scales, the trend of anticorrelation of the helium abundance with plasma β-parameter in the ICME is observed also. However, the dependences of the helium abundance on the plasma and magnetic field parameters can dynamically change at smaller scales. For example, several local medium-scale structures with a negative correlation of helium abundance and magnetic field magnitude can be observed on the background of positive correlation at large-scale structures.

References.

Yermolaev Y.I. et al., Catalog of large-scale solar wind phenomena during 1976–2000, Cosmic Res., 2009, vol. 47, no. 2, pp. 81–94

Yermolaev Y.I. et al., Dynamics of large-scale solar-wind streams obtained by the double superposed epoch analysis. 4. Helium abundance, Journal of Geophysical Research, 2020, 125 (7) https://doi.org/10.1029/2020JA027878

Khokhlachev A. A. et al., Variations of Protons and Doubly Ionized Helium Ions in the Solar Wind, Cosmic Research, 2021, vol. 59, no. 6, pp. 415-426
https://doi.org/10.1134/S0010952521060022

How to cite: Khokhlachev, A., Yermolaev, Y., Riazantseva, M., Rakhmanova, L., and Lodkina, I.: Dynamics of helium abundance inside and around ICME, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11326, https://doi.org/10.5194/egusphere-egu22-11326, 2022.

EGU22-4327 | Presentations | ST1.8 | Highlight

First results from the SO/PHI instrument on Solar Orbiter

Sami Khan Solanki, Julian Blanco, Fatima Kahil, Philipp Loeschl, Hanna Strecker, Johann Hirzberger, David Orozco Suárez, Jose Carlos Del Toro Iniesta, Joachim Woch, Achim Gandorfer, Alberto Alvarez-Herrero, Thierry Appourchaux, and Reiner Volkmer

The ESA/NASA Solar Orbiter mission, launched in February 2020, has just completed its cruise phase. During its nominal mission, it will explore the Sun and heliosphere from close up and from out of the ecliptic plane. It aims to address the overarching questions of how the Sun creates and controls the heliosphere, and why solar activity changes with time. Among the instruments onboard Solar Orbiter  is the Polarimetric and Helioseismic Imager (SO/PHI), which is the first magnetograph to leave the Sun-Earth line and to observe the Sun from different directions. Already during the cruise phase of Solar Orbiter, SO/PHI has provided a few glimpses of its capabilities, including the excellent quality of the data. In spite of the very limited amount of data gathered during cruise, a few interesting results have already been obtained. A selection of such results will be presented.

 

How to cite: Solanki, S. K., Blanco, J., Kahil, F., Loeschl, P., Strecker, H., Hirzberger, J., Orozco Suárez, D., Del Toro Iniesta, J. C., Woch, J., Gandorfer, A., Alvarez-Herrero, A., Appourchaux, T., and Volkmer, R.: First results from the SO/PHI instrument on Solar Orbiter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4327, https://doi.org/10.5194/egusphere-egu22-4327, 2022.

EGU22-4121 | Presentations | ST1.8

Spatial Structure of CIRs

Gergely Koban, Andrea Opitz, Zoltan Nemeth, Gabor Facsko, Akos Madar, Aniko Timar, Zsuzsanna Dalya, and Nikolett Biro

Co-rotating Interaction Regions are complex and fascianting structures in the Heliosphere that 
play an important role in space weather. They arise from the fast solar wind interacting with the 
slow solar wind streams. The interface between fast and slow solar wind is called the stream 
interface, and it is common for CIRs to produce forward shock at the leading edge and reverse 
shock at the trailing edge. CIRs often have considerable tilts in the north-south axis, owing to the magnetic 
conditions on the Sun.


Examination of the spatial structure of CIRs, – most importantly the aforementioned tilt – is not 
an easy task. We attempt a multi-spacecraft investigation in order to examine the spatial 
structure of CIRs on different distance scales. Using all available spacecraft data nearby, the tilt 
of the stream interface can be determined considering the time delays of the effects caused by 
the CIR recorded by each spacecraft. Our final aim is to improve solar wind propagation 
methods with these detailed CIR results.

How to cite: Koban, G., Opitz, A., Nemeth, Z., Facsko, G., Madar, A., Timar, A., Dalya, Z., and Biro, N.: Spatial Structure of CIRs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4121, https://doi.org/10.5194/egusphere-egu22-4121, 2022.

EGU22-1856 | Presentations | ST1.8

A Study of Small-Scale Brightenings using EUV Data from SPICE on board Solar Orbiter

Jenny Marcela Rodriguez Gomez, Peter Young, and Therese Kucera

Recently small-scale solar dynamic features have been observed on the Sun by Solar Orbiter/EUI (Berghmans et al. 2021; Panesar et al. 2021). These events (initially referred to as “campfires”) are small-scale heating events observed mainly in the solar corona. The Spectral Imaging of Coronal Environment (SPICE; SPICE Consortium et al. 2020) is a high-resolution imaging spectrometer that observes the Sun in extreme ultraviolet (EUV) wavelengths. This study uses L2 SPICE data (calibrated images)  to characterize and follow the evolution of these small-scale brightenings. Additionally, we use HRIEUV 174 Å on board Solar Orbiter and Stereo A datasets to have a complementary view of small-scale brightenings during the study period.

How to cite: Rodriguez Gomez, J. M., Young, P., and Kucera, T.: A Study of Small-Scale Brightenings using EUV Data from SPICE on board Solar Orbiter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1856, https://doi.org/10.5194/egusphere-egu22-1856, 2022.

EGU22-4155 | Presentations | ST1.8

Spatial variation of the background solar wind in the Inner Heliosphere

Nikolett Biro, Andrea Opitz, Zoltan Nemeth, Aniko Timar, Akos Madar, Gergely Koban, and Zsuzsanna Dalya
The importance of background solar wind is unquestionable as it carries information on the solar surface conditions and has a major role in space weather events. The current solar minimum is a perfect time period for investigations regarding this field, with several space probes providing in-situ measurements.
 
Our aim is to determine the spatial variations in the background solar wind through multi-spacecraft data analysis, including recent missions, such as Parker Solar Probe and Solar Orbiter. We adjust for the radial and longitudinal time-lags between the different spacecraft, then compare their solar wind plasma measurements. The effects of latitudinal differences between the observations is then backmapped to coronagraph imagery. The results will be useful for further analysis of inner heliospheric structures, for the improvement of propagation models, and to support the analysis of out-of-ecliptic solar wind observations.

How to cite: Biro, N., Opitz, A., Nemeth, Z., Timar, A., Madar, A., Koban, G., and Dalya, Z.: Spatial variation of the background solar wind in the Inner Heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4155, https://doi.org/10.5194/egusphere-egu22-4155, 2022.

EGU22-4182 | Presentations | ST1.8

The large-scale structure of the solar wind: flux conservation, radial scalings, Mach numbers, and critical distances 

Daniel Verscharen, Stuart D. Bale, and Marco Velli

One of the key challenges in solar and heliospheric physics is to understand the acceleration of the solar wind. As a super-sonic, super-Alfvénic plasma flow, the solar wind carries mass, momentum, energy, and angular momentum from the Sun into interplanetary space. We present a framework  based on two-fluid magnetohydrodynamics to estimate the flux of these quantities based on spacecraft data independent of the heliocentric distance of the location of measurement.

Applying this method to the Ulysses dataset allows us to study the dependence of these fluxes on heliolatitude and solar cycle. The use of scaling laws provides us with the heliolatitudinal dependence and the solar-cycle dependence of the scaled Alfvénic and sonic Mach numbers as well as the Alfvén and sonic critical radii. Moreover, we estimate the distance at which the local thermal pressure and the local energy density in the magnetic field balance.

These results serve as predictions for observations with Parker Solar Probe, which currently explores the very inner heliosphere, and Solar Orbiter, which will measure the solar wind outside the plane of the ecliptic in the inner heliosphere during the course of the mission.

How to cite: Verscharen, D., Bale, S. D., and Velli, M.: The large-scale structure of the solar wind: flux conservation, radial scalings, Mach numbers, and critical distances , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4182, https://doi.org/10.5194/egusphere-egu22-4182, 2022.

EGU22-2663 | Presentations | ST1.8

Extrapolation of solar wind parameters in three-dimensions in the inner heliosphere

Aniko Timar, Andrea Opitz, Gabor Facsko, Zsuzsanna Dalya, Gergely Koban, Nikolett Biro, Akos Madar, and Zoltan Nemeth

Solar wind parameters, such as the velocity, density or pressure of the solar wind, are one of the most important factors in space physics, and their knowledge at as many points in the heliosphere as possible contributes to a broader understanding of our solar system.

Solar wind parameters at various points in the inner heliosphere are estimated using extrapolation methods. Currently, all spacecraft measuring solar wind parameters are in the ecliptic plane, thus it is enough to extrapolate the data from space probes to other spacecraft or celestial bodies near the ecliptic. Solar Orbiter, on the other hand, will soon leave the ecliptic and reach heliocentric latitudes of 34 degrees by the end of the mission, opening a new perspective.

The ballistic method extrapolates solar wind parameters in one dimension from the point of measurement to a chosen heliospheric position. The simple ballistic model considers the average rotation period of the Sun for the extrapolation in longitude while assuming a constant solar wind velocity during radial propagation. Our improved solar wind propagation model takes into account the interaction of slow and fast solar wind by applying a pressure correction during the extrapolation.

Applying this pressure-corrected ballistic method to data from solar corona models, we determined the solar wind parameters in the heliosphere in three dimensions. The advantage of our pressure-corrected ballistic method is that it is simple, it requires little calculation and it can be easily applied to the data of solar corona models in order to obtain a fast and efficient prediction in three dimensions.

How to cite: Timar, A., Opitz, A., Facsko, G., Dalya, Z., Koban, G., Biro, N., Madar, A., and Nemeth, Z.: Extrapolation of solar wind parameters in three-dimensions in the inner heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2663, https://doi.org/10.5194/egusphere-egu22-2663, 2022.

EGU22-11163 | Presentations | ST1.8

Deriving proper electron characteristics in the solar wind from Solar Orbiter observations

Štěpán Štverák, Georgios Nicolaou, Christopher J. Owen, Milan Maksimovic, and Pavel M. Trávníček

Solar Orbiter, the latest ESA solar and heliospheric space mission, provides the most recent plasma measurements in the free streaming solar wind across a wide range of the radial distance from the Sun. Electron observations are enabled by the Electron Analyser System (EAS) being part of the Solar Wind Analyser (SWA) suit of instruments. Electron properties are measured in a form of velocity distribution functions (VDFs) with an unprecedent sampling rate of 10 s in the normal operational mode going down to even 8 Hz for limited burst mode snapshots. Regular EAS observations started in mid of 2020 and all data are being continuously made publicly available throughout the ESA's Solar Orbiter Archive (SOAR). Here we present some preliminary user-based methods and techniques of deriving proper electron characteristics from the Level 2 calibrated data set by calculating the required moments of measured VDFs. In particular, we focus on data correction with respect to possible instrument and/or spacecraft related effects. The obtained results are compared and validated by a cross calibration with respect to electron properties derived from the quasi-thermal noise measurements provided by the Radio and Plasma Waves (RPW) instrument, being also part of the in situ plasma payload of the Solar Orbiter mission.

How to cite: Štverák, Š., Nicolaou, G., Owen, C. J., Maksimovic, M., and Trávníček, P. M.: Deriving proper electron characteristics in the solar wind from Solar Orbiter observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11163, https://doi.org/10.5194/egusphere-egu22-11163, 2022.

EGU22-4987 | Presentations | ST1.8

Removal of false alarms from solar wind predictions

Zsuzsanna Dalya and Andrea Opitz

Solar wind propagation models using in situ plasma observations as input can be improved by removing the signatures of Interplanetary Coronal Mass Ejections (ICMEs) from the input data. ICMEs are sporadic events that propagate in a given direction, hence their signatures in the plasma data should not be extrapolated to other heliocentric longitudes. As a result, in order to improve the prediction accuracy these should be filtered out. We create dedicated ICME lists providing the exact start and end times of ICMEs to numerous space probes such as ACE, STEREO A&B, SOHO, WIND, SolO, PSP, DSCOVER, VEX, MEX, Rosetta, BepiColombo, MAVEN and Messenger. We provide solar wind plasma and magnetic field predictions to any inner heliospheric position applying the ICME filter on the input dataset this way eliminating false alarms such as false ICME signature forecasts. Our corrected predictions contribute to the investigation of the background solar wind and related fields.

How to cite: Dalya, Z. and Opitz, A.: Removal of false alarms from solar wind predictions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4987, https://doi.org/10.5194/egusphere-egu22-4987, 2022.

EGU22-6620 | Presentations | ST1.8

Directional Discontinuities in the Inner Heliosphere

Ákos Madár, Geza Erdos, Andrea Opitz, Zoltan Nemeth, Gabor Facsko, Aniko Timar, Nikolett Biro, Gergely Koban, and Zsuzsa Dalya

The Parker Solar Probe and Solar Orbiter spacecraft make whole new spatial and time scales available in the inner Heliosphere. With these new data, we study directional discontinuities that are common structures in the solar wind in this region. Their radial distribution can provide insight into the physical processes of this virtually collisionless plasma. Applying a method (Erdős & Balogh, 2008) based on minimum variance analysis to select directional discontinuities in magnetic field data, we determine their number as a function of distance from the Sun. How the directional discontinuity occurrence rate depends on the solar wind speed is also part of our analysis.

How to cite: Madár, Á., Erdos, G., Opitz, A., Nemeth, Z., Facsko, G., Timar, A., Biro, N., Koban, G., and Dalya, Z.: Directional Discontinuities in the Inner Heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6620, https://doi.org/10.5194/egusphere-egu22-6620, 2022.

EGU22-3464 | Presentations | ST1.8

The role of coronal shocks for accelerating solar energetic electrons

Nina Dresing, Athanasious Kouloumvakos, Rami Vainio, and Alexis Rouillard

We study the role of Coronal Mass Ejection (CME)-driven shocks in the acceleration of solar energetic electrons. Using observations by the two STEREO spacecraft, we correlate electron peak intensities of solar energetic particle events measured in situ with various parameters of the associated coronal shocks. These shock parameters were derived by combining 3D shock reconstructions with global modeling of the corona. This technique provides also shock properties in the specific shock regions that are magnetically connected to the two STEREO spacecraft. We find significant correlations between the peak intensities and the Mach number of the shock with correlation coefficients of about 0.7, which are similar for electrons at ∼ 1 MeV and protons at > 60 MeV. Lower energy electrons < 100 keV show a smaller correlation coefficient of 0.47. The causal relationship between electron intensities and the shock properties is supported by the vanishing correlations, when peak intensities at STEREO-A are related with the Alfvénic Mach numbers at the magnetic footpoint of STEREO-B and vice versa, which yields correlation coefficients of 0.03 and -0.13 for ∼ 1 MeV and < 100 keV electron peak intensities, respectively. We conclude that the high-energy electrons are accelerated mainly by the shock, while the low energy electrons are likely produced by a mixture of flare and shock-related acceleration processes.

How to cite: Dresing, N., Kouloumvakos, A., Vainio, R., and Rouillard, A.: The role of coronal shocks for accelerating solar energetic electrons, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3464, https://doi.org/10.5194/egusphere-egu22-3464, 2022.

EGU22-6726 | Presentations | ST1.8