ST1.1

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.