Displays

At some level, magnetic reconnection functions by means of a balance between current dissipation, and current maintenance due to the reconnection electric field. While this dissipation is well understood process in symmetric magnetic reconnection, the way nonideal electric fields interact with the current density in asymmetric reconnection is still unclear. In symmetric reconnection, the current density maximum, the X point location, and the nonideal electric field determined by the divergence of the electron pressure tensor usually coincide. In asymmetric reconnection, however, the electric field at the X point can be partly provided by bulk inertia terms, implying that the X point cannot be the dominant location of dissipation. On the other hand, we know that the nongyrotropic pressure-based electric field must dominate at the stagnation point of the in-plane electron flow, and that electron distributions here feature crescents. The further fact that the current density peak is shifted off the position of the X point indicates that there may be a relation between this current density enhancement, the location of the stagnation point, and the electron nongyrotropies. In this presentation we report on further progress investigating the physics of the electron diffusion region in asymmetric reconnection with a focus on how to explain the dissipation operating under these conditions. 

How to cite: Hesse, M., Norgren, C., Tenfjord, P., Burch, J., Liu, Y.-H., Chen, L.-J., Bessho, N., Spinnangr, S., and Kolstø, H.: How does dissipation work in the electron diffusion region of asymmetric magnetic reconnection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5435, https://doi.org/10.5194/egusphere-egu2020-5435, 2020.

Magnetic reconnection is a fundamental process for many plasma phenomena converting the stored magnetic energy into kinetic energy, thermal energy, and particle acceleration energy. Various missions have been launched, the latest being Magnetospheric Multiscale Mission (MMS), to improve the understanding of reconnection with in-situ measurements. In particular, particle distributions provide a rich insight on the local physics but a unique specific distribution cannot be used as a signature for reconnection as it does not reflect the phenomenon for all the possible external conditions. For instance, a strong anisotropy can be observed near the electron exhaust [1] while crescent-shaped distributions can be detected near the electron stagnation point for asymmetric reconnection [2].

From Particle-In-Cells (PIC) simulations, we developed a detection algorithm using a machine learning technique called Gaussian Mixture Model approximating the underlying density function by a sum of Gaussians [3]. The objective is twofold: finding a good approximation for the distribution while keeping a statistical meaning to the different components of the sum. The deviation from classical Maxwellians and the distributions with complex shapes provide a good measurement to identify reconnection. The algorithm was successfully applied to 2.5D simulations and large regions around the diffusion region and the separatrix were spotted. Different kinds of distributions have been efficiently identified.

The presented results tend to extend this method to other sources of data:

1. 3D simulations: although reconnection in 2D is well understood, many unanswered questions persist for 3D systems. Usually, such simulations show regions of millions of kilometers while having a sufficient resolution to be able to observe the tiny regions in which the original reconnection events occur. A deep analysis and understanding of these very large simulations appear as very challenging. Therefore, we expect that our method supports the analysis by automatically identifying various regions of interest with potential reconnection.
2. observational data: as the model has been validated on simulations, we are interested to apply the method on real data from the MMS mission. Will the observations made by scientists of the mission compare with the result of a fully automatic tool? In particular, the data pre-processing providing cleaned and readable data to the algorithm is very challenging.

In conclusion, the Gaussian Mixture Model approach is a first attempt to automatically characterize various kinetic behaviors encountered in both numerical simulations and space missions. In particular, it represents a very good potential to support data analysis of spacecraft observations but also fully three-dimensional simulations.

This contribution has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 776262 (AIDA, ).

[1] Shuster et al. “Highly structured electron anisotropy in collisionless reconnection exhausts”, 2014, Geophysical Research Letters, 41, 5389

[2] Burch et al., “Electron-scale measurements of magnetic reconnection in space.”, 2016b, Science, vol. 352, no 6290, p. aaf2939

[3] Dupuis et al., “Characterizing magnetic reconnection regions using Gaussian mixture models on particle velocity distributions”, 2020, ApJ, accepted,

How to cite: Dupuis, R., Amaya, J., Lapenta, G., Goldman, M., and Newman, D.: Automated characterization of magnetic reconnection using particle distributions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15156, https://doi.org/10.5194/egusphere-egu2020-15156, 2020.

We investigate the scattering of strahl electrons by microinstabilities as a mechanism for creating the electron halo in the solar wind. We develop a mathematical framework for the description of electron-driven microinstabilities and discuss the associated physical mechanisms. We find that an instability of the oblique fast-magnetosonic/whistler (FM/W) mode is the best candidate for a microinstability that scatters strahl electrons into the halo. We derive approximate analytic expressions for the FM/W instability threshold in two different β_c regimes, where β_c is the ratio of the core electrons' thermal pressure to the magnetic pressure, and confirm the accuracy of these thresholds through comparison with numerical solutions to the hot-plasma dispersion relation. We find that the strahl-driven oblique FM/W instability creates copious FM/W waves under low-β_c conditions when U_0s>3w_c, where U_0s is the strahl speed and w_c is the thermal speed of the core electrons. These waves have a frequency of about half the local electron gyrofrequency. We also derive an analytic expression for the oblique FM/W instability for β_c~1. The comparison of our theoretical results with data from the Wind spacecraft confirms the relevance of the oblique FM/W instability for the solar wind. In addition, we find a good agreement between our theoretical results and numerical solutions to the quasilinear diffusion equation. We make predictions for the electron strahl close to the Sun, which will be tested by measurements from Parker Solar Probe and Solar Orbiter.

How to cite: Verscharen, D., Jeong, S.-Y., Chandran, B., Salem, C., Pulupa, M., and Bale, S.: Kinetic theory and simulation of electron-strahl scattering in the solar wind, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2165, https://doi.org/10.5194/egusphere-egu2020-2165, 2020.

We analyzed properties of waves excited by mildly relativistic electron beams propagating along magnetic field with a ring-shape perpendicular momentum distribution in neutral and current-free solar coronal plasmas. These plasmas are subject to both the beam and the electron cyclotron maser (ECM) instabilities driven by the positive momentum gradient of the ring-beam electron distribution in the directions parallel and perpendicular to the ambient magnetic field, respectively. To explore the related kinetic processes self-consistently, 2.5-dimensional fully kinetic particle-in-cell (PIC) simulations were carried out.

To quantify excited wave properties in different coronal conditions, we investigated the dependence of their energy and polarization on the ring-beam electron density and magnetic field. In general, electrostatic waves dominate the energetics of waves and nonlinear waves are ubiquitous. In weakly magnetized plasmas, where the electron cyclotron frequency ω_ce is lower than the electron plasma frequency ω_pe, it is difficult to produce escaping electromagnetic waves with frequency ω > ω_pe and small refractive index ck/ω < 1 (k and c are the wavenumber and the light speed, respectively). Highly polarized and anisotropic escaping electromagnetic waves can, however, be effectively excited in strongly magnetized plasmas with ω_ce/ω_pe ≥ 1. The anisotropy of the energy, circular polarization degree (CPD), and spectrogram of these escaping electromagnetic waves strongly depend on the number density ratio of the ring-beam electrons to the background electrons. In particular, their CPDs can vary from left-handed to right-handed with the decrease of the ring-beam density, which may explain some observed properties of solar radio bursts (e.g., radio spikes) from the solar corona.

How to cite: Zhou, X., Munoz Sepulveda, P., Buechner, J., and Liu, S.: Coherent emission driven by energetic ring-beam electrons in the solar corona, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2532, https://doi.org/10.5194/egusphere-egu2020-2532, 2020.

The role of turbulence is one of key issues for understanding the magnetic and plasma energy conversion, plasma heating and high energy particles acceleration in large temporal-spatial scale turbulent magnetic reconnection (LTSTMR; observed current sheet thickness to characteristic electron length, Larmor radius for low-beta and electron inertial length for high-beta, ratios on the order of ten to the power of ten or higher; observed evolution time to electron cyclotron time ratios on the order of ten to the power of ten or higher) . Solar atmosphere activities (e.g., limbs, flares, coronal mass ejections, solar winds and so on), which are the most important phenomenon in the solar and Sun-Earth space systems, are typical LTSTMRs.

Here we used our newly developed RHPIC-LBM algorithm[*]  to perform the role of  turbulence in the magnetic fluctuation-induced self-generating-organization  (MF-ISGO), the turbulence in the plasma turbulence-induced self-feeding-sustaining (PT-ISFS), and the interaction of turbulence between MF-ISGO and PT-ISFS in the continuous kinetic-dynamic-hydro fully coupled LTSTMR. 

First, we find that the self-generated turbulence by magnetic field and plasma motion collective interaction include two fully coupled processes of 1) fluid vortex induced magnetic reconnection (MR) and 2) MR induced fluid vortex. The Biermann battery effect and  alpha-effect can not only generate magnetic fields, but can server them to trigger MR, the Spitzer resistance and turbulence resistance (beta-effect)  can not only generate magnetic eddies, but can server  them to trigger fluid turbulence.  

Then, we find that these interaction leads to vortex splitting and phase separating instabilities, and there are four species instabilities coexist in the evolution process. 1) Vortex separation interface instabilities. 2)Magnetic fluctuation-induced self-generating-organization instabilities. 3) Plasma turbulence-induced self-feeding-sustaining instabilities. 4) Vortex shedding instabilities.

Finally, the nuanced details of the magnetic topological structure and the topological characterization of flow structures in plasma of the simulated 3D LTSTMR are also presented.

The characterization of turbulence anisotropy and the turbulence acceleration of the LTSTMR are presented in Part II and Part III of this three-paper series study.

*Techniques and algorithms for RHPIC-LBM have been developed in previous studies (e.g.,Zhu2020a, Zhu2020b)

References

Zhu, B. J., Yan, H., Zhong, Y., et al. 2020a, Appl Math Model, 78, 932, doi: 10.1016/j.apm.2019.09.043

Zhu, B. J., Yan, H., Zhong, Y., et al. 2020b, Appl Math Model, 78, 968,doi: 10.1016/j.apm.2019.05.027

How to cite: Zhu, B., Yan, H., Cheng, H., Zhong, Y., Du, Y., and Yuen, D. A.: Self-generated turbulence by plasmas and magnetic field collective interaction in 3D large temporal-spatial turbulent magnetic reconnection: I. The Basic Feature, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7950, https://doi.org/10.5194/egusphere-egu2020-7950, 2020.

One of the outstanding open questions in space plasma physics is the heating problem in the solar corona and the solar wind. In-situ measurements, as well as MHD and kinetic simulations, suggest a relation between the turbulent nature of plasma and the onset of magnetic reconnection as a channel of energy dissipation, particle acceleration and a heating mechanism. It has also been proven that non-linear interactions between counter propagating Alfvén waves drives plasma towards a turbulent state. On the other hand, the interactions between particles and waves becomes stronger at scales near the ion(electron) gyroradious ρi (ρe ), and so turbulence can enhance conditions for reconnection and increase the number of reconnection sites. Therefore, there is a close link between turbulence and reconnection. We use fully kinetic particle in cell (PIC) simulations, able to resolve the kinetic phenomena, to study the onset of reconnection in a 3D simulation box with parameters similar to the solar wind under Alfvénic turbulence. We identify in our simulations characteristic features of reconnection sites as steep gradients of the magnetic field strength alongside with the formation of strong current sheets and inflow-outflow patterns of plasma particles near the diffusion regions. These results will be used to quantify the role reconnection in plasma turbulence.

How to cite: Agudelo Rueda, J. A., Verscharen, D., Wicks, R., Owen, C., Nicolaou, G., Walsh, A., Zouganelis, Y., and Vargas, S.: Identifying and Quantifying the Role of Magnetic Reconnection in Space Plasma Turbulence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3573, https://doi.org/10.5194/egusphere-egu2020-3573, 2020.

Turbulence in space and astrophysical plasmas is an intrinsically chaotic and multiscale phenomenon that involves nonlinear coupling across different temporal and spatial scales. There is growing evidence that plasma instabilities, such as magnetic reconnection taking place in localized current sheets, enhance the energy dissipation toward small sub-ion scales. However, it is hotly debated whether the dominant contribution to the scale-to-scale energy transfer at kinetic scales is due to non-linear wave interactions or to coherent structures. Here we present the results from a multiscale study of 2D Hall-MHD and hybrid Particle-in-cell (PIC) numerical simulations of decaying turbulence, performed by means of Multidimensional Iterative Filters (MIF), a new technique developed for the spatio-temporal analysis of non-stationary non-linear multidimensional signals. Results show that, at the maximum of turbulent activity, the power spectrum of magnetic fluctuations at sub-ion scales is formed by localized structures and/or perturbations with temporal frequencies smaller than the ion-cyclotron frequency. Going toward smaller kinetic scales, the contribution of low-medium frequency perturbations to the magnetic spectrum becomes important. However, the dispersion relation and polarization properties of such perturbations are not consistent with those of Kinetic Alfvèn Waves (KAW). We conclude that the dynamics of turbulence at sub-ion scales is mainly shaped by localized intermittent structures, with no apparent contribution of KAW-like interactions at small scales.

How to cite: Papini, E., Cicone, A., Piersanti, M., Franci, L., Landi, S., and Hellinger, P.: Multiscale analysis of Hall-MHD and Hybrid-PIC simulations of plasma turbulence: structures or waves?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19295, https://doi.org/10.5194/egusphere-egu2020-19295, 2020.

Electric field properties of the kinetic Alfvén mode are analytically studied by constructing the dielectric tensor of the plasma using the linear Vlasov theory and reducing (and identifying) the tensor elements into that of the fluid picture such as the polarization drift, the Hall current, and the diamagnetic current. Off-diagonal dielectric responses do not primarly contribute to the dispersion relation of the kinetic Alfvén mode, but play an important role in the electric field polarization (field rotation sense around the mean magnetic field) and parallel component of the field. The polarization becomes more circular and the parallel component enhances at larger perpendicular wavenumbers. Analytic expression of fluctuation sense serves as a tool to identify the kinetic Alfvén mode in space plasma observations.

How to cite: Narita, Y., Vörös, Z., Roberts, O. W., and Hoshino, M.: Transport ratios of the kinetic Alfvén mode in space plasmas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4108, https://doi.org/10.5194/egusphere-egu2020-4108, 2020.

Solar flares originate from the release of the energy stored in the magnetic field of solar active regions. Generally, the photospheric magnetograms of active regions are used as the input of the solar flare forecasting model. However, solar flares are considered to occur in the low corona. Therefore, the role of 3D magnetic field of active regions in the solar flare forecast should be explored. We extrapolate the 3D magnetic field using the potential model for all the active regions during 2010 to 2017, and then the deep learning method is applied to extract the precursors of solar flares in the 3D magnetic field data. We find that the 3D magnetic field of active regions is helpful to build a deep learning based forecasting model.

How to cite: Huang, X.: Solar flare forecasting model using 3D magnetic field data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13298, https://doi.org/10.5194/egusphere-egu2020-13298, 2020.

How to cite: Zhu, X. and Wiegelmann, T.: Magnetohydrostatic modelling of the solar atmosphere: Test and application, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2695, https://doi.org/10.5194/egusphere-egu2020-2695, 2020.

 It is well-known that there is a gradient, there will drive a flow inevitably. For example, a density-gradient may drive a diffusion flow, an electrical potential-gradient may drive an electric current in plasmas, etc. Then, what flows will be driven when a magnetic-gradient occurs in solar atmospheric plasmas?

Considering the ubiquitous distribution of magnetic-gradient in solar plasma loops, this work demonstrates that magnetic-gradient pumping (MGP) mechanism is valid even in the partial ionized solar photosphere, chromosphere as well as in the corona. MGP drives energetic particle flows which carry and convey kinetic energy from the underlying atmosphere to move upwards, accumulate around the looptop and increase there temperature and pressure, and finally lead to eruptions around the looptop by triggering ballooning instabilities. This mechanism may explain the evolution of solar plasma loops, the formation of the observing hot cusp-structures above flaring loops in most preflare phases, and the triggering of eruptions in solar plasma loops. Therefore, the magnetic-gradient may play as a natural driver of solar eruptions.

Furthermore, we may also apply MGP mechanism to understand many other astrophysical phenomena, such as the coronal heating, the temperature distribution above sunspots, the formation of solar plasma jets, type-II spicule, and fast solar wind above coronal holes, as well as the fast plasma jets related to white dwarfs, neutron stars and black holes.

Additionally, we also proposed to test the above MGP mechanism by using the new generation observations of the broadband spectral radioheliographs, such as MUSER, EVOSA, and SRH, etc.

How to cite: Tan, B.: Magnetic Gradient May Play as a Natural Driver of Solar Eruptions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22259, https://doi.org/10.5194/egusphere-egu2020-22259, 2020.

In order to study the evaporation of chromospheric plasma and the formation of hard X-ray (HXR) sources in solar flare events, we coupled an analytic energetic electron model with the multi-dimensional MHD simulation code MPI-AMRVAC. The transport of fast electrons accelerated in the flare looptop is governed by the test particle beam approach reported in Emslie et al. (1978), now used along individual field lines. Anomalous resistivity, thermal conduction, radiative losses and gravity are included in the MHD model. The reconnection process self-consistently leads to formation of a flare loop system and the evaporation of chromospheric plasma is naturally recovered. The non-thermal HXR emission is synthesized from the local fast electron spectra and local plasma density, and thermal bremsstrahlung soft X-ray (SXR) emission is synthesized based on local plasma density and temperature. We found that thermal conduction is  an efficient way to trigger evaporation flows. We also found that the generation of a looptop HXR source is a result of fast electron trapping, as evidenced by the pitch angle evolution. By comparing the SXR flux and HXR flux, we found that a possible reason for the “Neupert effect” is that the increase of non-thermal and thermal energy follows the same tendency.

How to cite: Ruan, W. and Keppens, R.: MHD simulation of solar flare by applying analytical energetic fast electron model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4982, https://doi.org/10.5194/egusphere-egu2020-4982, 2020.

Knowledge about the magnetic field and plasma environment is important
for almost all physical processes in the solar atmosphere. Precise
measurements of the magnetic field vector are done routinely only in
the photosphere, e.g. by SDO/HMI. These measurements are used as
boundary condition for modelling the solar chromosphere and corona,
whereas some model assumptions have to be made. In the low-plasma-beta
corona the Lorentz-force vanishes and the magnetic field
is reconstructed with a nonlinear force-free model. In the mixed-beta
chromosphere plasma forces have to be taken into account with the
help of a magnetostatic model. And finally for modelling the global
corona far beyond the source surface the solar wind flow has to
be incorporated within a stationary MHD model.
To do so, we generalize a nonlinear force-free and magneto-static optimization
code by the inclusion of a field aligned compressible plasma flow.
Applications are the implementation of the solar wind on
global scale. This allows to reconstruct the coronal magnetic field further
outwards than with potential field, nonlinear force-free and magneto-static models.
This way the model might help in future to provide the magnetic connectivity
for joint observations of remote sensing and in-situ instruments on Solar
Orbiter and Parker Solar Probe.

How to cite: Wiegelmann, T., Neukirch, T., Nickeler, D., and Chifu, I.: An optimization principle for computing stationary MHD equilibria with solar wind flow, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3029, https://doi.org/10.5194/egusphere-egu2020-3029, 2020.

How to cite: Zhu, X., He, J., Duan, D., Zhang, L., Yang, L., Hou, C., and Ying, W.: Possible Generation Mechanism for Alfvenic Velocity Spikes and Magnetic Field Switchbacks as Observed by PSP, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18832, https://doi.org/10.5194/egusphere-egu2020-18832, 2020.

The stability of contact discontinuities formed by the relaxation of two Maxwellian plasmas with different number densities but the same plasma thermal pressure is studied by means of a one-dimensional electrostatic full-Vlasov simulation. Our simulation runs with various combinations of ion-to-electron ratios of the high-density and low-density regions showed that transition layers of density and temperature without jump in the plasma thermal pressure are obtained when the electron temperatures in the high-density and low-density regions are almost equal to each other. However, the stable structure of the contact discontinuity with a sharp transition layer on the Debye scale is not maintained. It is suggested that non-Maxwellian velocity distributions are necessary for the stable structure of contact discontinuities. A direct comparison between full- and hybrid-Vlasov simulations is also made.

How to cite: Umeda, T., Tsujine, N., and Nariyuki, Y.: Kinetic Vlasov simulations of contact discontinuities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-48, https://doi.org/10.5194/egusphere-egu2020-48, 2020.

The electron heat flux is one of the leading terms in energy flow processes in the collisionless or weakly-collisional solar wind plasma. The very first observations demonstrated that the collisional Spitzer-HÓ“rm law could not describe the heat flux in the solar wind well. In particular, in-situ observations at 1AU showed that the heat flux was suppressed below the collisional value. Different mechanisms of the heat flux regulation in the solar wind were proposed. One of these possible mechanisms is the wave-particle interaction with whistler-mode waves produced by the so-called whistler heat flux instability (WHFI). This instability operates in plasmas with at least two counter-streaming electron populations. Recent observations indicated that the WHFI operates in the solar wind producing predominantly quasi-parallel whistler waves with the amplitudes up to several percent of the background magnetic field. But whether such whistler waves can regulate the heat flux still remained an open question.

We present the results of simulation of the whistler generation and nonlinear evolution using the 1D full Particle-in-Cell code TRISTAN-MP. This code models self-consistent dynamics of ions and two counter-streaming electron populations:  warm (core) electrons and hot (halo) electrons. We performed two sets of simulations. In the first set, we studied the wave generation for the classical WHFI, so both core and halo electron distributions were taken to be isotropic. We found a positive correlation between the plasma beta and the saturated wave amplitude. For the heat flux, the correlation changes from positive to a negative one at some value of the heat flux. The observed wave amplitudes and correlations are consistent with the observations. Our calculations show that the electron heat flux does not change substantially in the course of the WHFI development; hence such waves are unlikely to contribute significantly to the heat flux regulation in the solar wind.

The classical WHFI drives only those whistler waves that propagate along the halo electron drift direction (consequently, parallel with respect to background magnetic field). Such waves interact resonantly with electrons that move in the opposite direction; hence, only a relatively small fraction of hot halo electrons is affected by these waves. On the contrary, anti-parallel whistler waves would interact with a substantial fraction of halo electrons. Thus, they could influence the heat flux more significantly. To test this hypothesis, we performed the second set of simulations with anisotropic halo electrons. Anisotropic distribution drives both parallel and anti-parallel waves. Our calculations demonstrate that anti-parallel whistler waves can decrease the heat flux. This indicates that the waves generated via combined whistler anisotropy and heat flux instabilities might contribute to regulation of the heat flux in the solar wind.

The work was supported by NSF grant 1502923. I. Kuzichev would also like to acknowledge the support of the RBSPICE Instrument project by JHU/APL sub-contract 937836 to the New Jersey Institute of Technology under NASA Prime contract NAS5-01072. Computational facility: Cheyenne supercomputer (doi:10.5065/D6RX99HX) provided by NCAR’s Computational and Information Systems Laboratory, sponsored by NSF

How to cite: Kuzichev, I., Vasko, I., Soto-Chavez, A. R., and Artemyev, A.: Role of Whistler Waves in Regulation of the Heat Flux in the Solar Wind , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1175, https://doi.org/10.5194/egusphere-egu2020-1175, 2020.

Magnetohydrodynamic waves in a stratified rotating plasma in a gravitational field in the Boussinesq approximation are studied. The theory of flows on the f -plane, on the non-traditional f-plane (taking into account the horizontal component of the Coriolis force), on the beta -plane, and on the non-traditional beta -plane is developed. In each considered case linear solutions of systems of three-dimensional magnetohydrodynamic equations in the Boussinesq approximation are obtained in form of magnetic inertio-gravity waves, magnetostrophic waves, and magneto-Rossby waves. For equations of a rotating stratified plasma without taking into account sphericity (in the approximation of the f-plane and the non-traditional f- plane), dispersion relations describe three-dimensional magnetic inertio-gravity waves and three-dimensional magnetostrophic waves. In the case of propagating only along the vertical component of the wave vector, their dispersion relations describe two types of magnetic waves, the first of which is a special case of magnetic inerto-gravity waves propagating only vertically, and the second is a special case of magnetostrophic waves propagating only vertically. In addition, it was found that dispersion relations describing wave propagation taking into account sphericity in a first approximation (on the beta-plane and on the non-traditional beta- plane) along the vertical component of the wave vector have a similar particular form. In the case of wave propagation in a horizontal plane, magnetic inertio-gravity waves turn into Alfvén waves, and magnetostrophic waves turn into magnetogravitational waves. In addition, for waves on a non-traditional f-plane, the influence of the horizontal component of the Coriolis force on the existence of various types of three-wave interactions is shown. For equations of a rotating stratified plasma on the beta-plane and on the non-traditional beta-plane dispersion relations for horizontal waves are found in form of magnetogravitational waves (similar to waves on the f- plane) and various types of magneto-Rossby waves. In addition, the equivalence of the low-frequency mode of the magneto-Rossby wave in the Boussinesq approximation and in the magnetohydrodynamic shallow water approximation was shown. The dispersion curves of all the detected wave types are qualitatively analyzed to identify the fulfillment of the synchronism condition, which ensures the presence of three-wave interactions. A system of amplitude equations for interacting waves and the increments of two types of instability that occur in the system (decay and amplification) are obtained using the method of multiscale expansions. The difference in the coefficients and differential operators in the three-wave interaction system is shown for each of the found types of three-wave interactions.

This research was supported by the Russian Foundation for Basic Research (project no. 19-02-00016)

How to cite: Fedotova, M. and Petrosyan, A.: Linear and nonlinear waves in three-dimensional stratified rotating astrophysical flows in the Boussinesq approximation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1540, https://doi.org/10.5194/egusphere-egu2020-1540, 2020.

A significant number of observed flows in geophysics, astrophysics, and laboratory experiments are in a state of magnetohydrodynamic turbulence. Among them are flows in the Earth’s outer core, in plasma shells of Earth, planets, and satellites of the solar system with strong magnetic fields, as well as flows in the Sun, stars, and astrophysical disks. Despite significant advances in the study of turbulence under the conditions typical of thermonuclear fusion devices, studies of the fundamental properties of homogeneous turbulence in rotating magnetohydrodynamic flows are still fragmentary and mainly concern turbulence in astrophysical disks, the solar tachocline and convective region of the Sun, and two-dimensional magnetohydrodynamic flows on the β-plane. Only in a few exceptional works were the properties of magnetohydrodynamic turbulence studied by simple analytical methods using Fourier series for similarity parameters, characteristic of the Earth’s core.

The aim of this work is to study the influence of the interaction of Alfvén wave packets on the dynamics of homogeneous turbulence. The method of calculation o magnetohydrodynamic turbulence we developed allows numerical simulation at large characteristic times and large external magnetic fields. The proposed method of setting the initial conditions for the velocity field makes it possible to satisfy the divergence-free, homogeneity, and turbulence isotropy conditions, as well as to set an arbitrary spectral distribution of the energy at the initial time without additional calculations. Numerical experiments demonstrate a nontrivial behavior of turbulent kinetic and magnetic energies. It is shown that periodic imbalance in energies occurs in the system in the form of conversion of kinetic energy into magnetic energy and vice versa. The analysis of the results shows that the detected nontrivial temporal dynamics of turbulence is caused by the periodic collisions of Alfvén wave packets.

This work was supported by the Russian Foundation for Basic Research (project no. 19-02-00016).

How to cite: Sirazov, R. and Petrosyan, A.: Periodic imbalances of kinetic and magnetic energies in rotating magnetohydrodynamic turbulent flows, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3454, https://doi.org/10.5194/egusphere-egu2020-3454, 2020.

Numerical studies of two-dimensional β-plane homogeneous magnetohydrodynamic turbulence are presented. The study of the fundamental properties of such turbulence allows understanding the evolution of various astrophysical objects from the Sun and stars to planetary systems, galaxies, and galaxy clusters. Energy spectra and cascade process in two-dimensional β-plane MHD are studied.

In this work the equations of two-dimensional magnetohydrodynamics with the Coriolis force in the β-plane approximation are used for the qualitative analysis and numerical simulation of processes in plasma astrophysics. The equations are solved on a square box of edge size 2π with periodic boundary conditions applying a the pseudospectral method using the 2/3 rule for dealiasing. The results of numerical simulation of two-dimensional β-plane MHD turbulence with a spatial resolution of 1024 × 1024 and 4096 × 4096 with different Rossby parameters β and different Reynolds numbers are presented.

It is found that only unsteady zonal flows with complex temporal dynamics are formed in two-dimensional β-plane magnetohydrodynamic turbulence. It is shown that flow nonstationarity is due to the appearance of isotropic magnetic islands caused by the Lorentz force in the system. The formation of Iroshnikov–Kraichnan spectrum is shown in the early stages of evolution of two-dimensional β-plane magnetohydrodynamic turbulence. The self-similarity of the decay of Iroshnikov–Kraichnan spectrum is studied. On long time scale violation of self-similarity of the decay and formation of Kolmogorov spectrum is discovered. The inverse cascade of kinetic energy, which is characteristic of the detected Kolmogorov spectrum, provides the formation of zonal flows.

This work was supported by the Russian Foundation for Basic Research (project no. 19-02-00016).

How to cite: Zinyakov, T. and Petrosyan, A.: Inverse cascade of kinetic energy in two-dimensional β-Plane magnetohydrodynamic turbulence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4497, https://doi.org/10.5194/egusphere-egu2020-4497, 2020.

In this report, we present a prominence observed by New Vacuum Solar Telescope (NVST) in Hα wavelength.  We use morphological approach to identify the rising or descending knots in the prominence. The rising knots are often found on the top of the prominence, while more knots are seen to descend from anywhere of the prominence.

The optical flow, referring to the apparent proper motion of a feature across the image plane, may be used to determine the velocity field from two images. The technique of local correlation tracking (LCT) optical flow has been widely used in the solar research. The Demon algorithm, which has been  used to match medical image, performs image-to-image matching by determining the optical flow between two images. We have examined the performance of the two methods applying the Hα images, and we noted that the Demon algorithm outperforms traditional LCT  methods.

The result of Demon optical flow allows us to estimate the velocity and acceleration of the moving knots. The descending speed of the knots near the solar surface is higher than that far away from the solar surface. This indicate that most of knots are more possible to descend across the horizontal magnetic field.

How to cite: Bi, Y.: Dynamics of moving knots in a solar prominence observed by New Vacuum Solar Telescope, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8362, https://doi.org/10.5194/egusphere-egu2020-8362, 2020.

In this report we study statistical properties of astrophysical turbulent plasma flows subjected to large scale velocity shear and an external magnetic field using Rapid Distortion Theory (RDT). The problem of shear-driven turbulence arises in several important physical systems, such as the solar wind and ionized atmospheres of exoplanets. Rapid distortion theory is a linearization method for Reynolds-averaged Navier-Stockes equations. Its main assumption is that the turbulence responds to the external distortion by velocity shear so fast, that inertial forces result in a negligible change in velocity field statistics at small time scales. This allows to linearize equations and to derive equations for second moments of turbulence. We apply RDT approach to incompressible homogeneous MHD turbulence distorted with an external magnetic field and a linear velocity shear in cases of rotating and non-rotating plasma. It is shown that even with a strong nonlinearity many properties of turbulence can be qualitatively studied using a linear theory. A closed system of linear equations is derived for energy, helicity and polarization of velocity and magnetic field correlations. Structural analysis is conducted showing the change of energy distribution between components of spectral tensor of turbulence. Development of initially isotropic turbulence and transition to anisotropy are studied. Model equations for fluid, current and cross helicity are derived. Differences in cases of rotating and non-rotating flows are discussed. This work was supported by the Russian Foundation for Basic Research (project no. 19-02-00016).

How to cite: Safonov, S. and Petrosyan, A.: Rapid distortion theory for homogeneous shear-driven MHD turbulence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8646, https://doi.org/10.5194/egusphere-egu2020-8646, 2020.

This study is devoted to the development of the nonlinear theory of the magneto-Poincare waves and magnetostrophic waves in rotating layers of astrophysical and space plasma in the shallow-water approximation. These waves determine the large-scale dynamics of the various astrophysical and space objects such as solar tachocline, as well as  magnetoactive atmospheres of exoplanets trapped by tides of a carrier star, neutron stars atmospheres and the flows in accretion disks of neutron stars. For this purpose we derived magnetohydrodynamic shallow water equations with a rotation and presence of an external vertical magnetic field. The system is obtained from conventional magnetohydrodynamic equations for incompressible inviscid heavy plasma layer with free surface in an external vertical magnetic field. The pressure is assumed to be hydrostatic, and the height of the plasma layer is considered to be much smaller than horizontal scales of the flow. The magnetohydrodynamic equations in the shallow-water approximation play equally important role in the space and astrophysical plasma flows like classical shallow-water equations in the fluid dynamics of a neutral fluid. The magnetohydrodynamic shallow water equations with an external vertical magnetic field are modified by supplementing them with the equation for the vertical component of the magnetic field and divergence-free condition for magnetic field contains its vertical component. Thus the velocity field remains two-dimensional while the magnetic field becomes three-dimensional. It is shown that the presence of a vertical magnetic field significantly changes the dynamics of the wave processes in astrophysical plasma compared to the neutral fluid and plasma layer in a horizontal magnetic field.  We have investigated the interaction of Magneto-Poincare waves and magnetostrophic waves in the magnetohydrodynamic shallow water flows in external vertical magnetic field and in horizontal (toroidal and poloidal) magnetic field. In the absence of the horizontal magnetic field the dynamics of plasma appears to be similar to the neutral fluid dynamics and it is shown that there are four-waves interactions in this case. Using the asymptotic multiscale method we obtained the non-linear amplitude equations for the three interacting Magneto-Poincare waves and magnetostrophic waves. The analysis of the amplitude equations shows that there are two types of instabilities for four different types of three-waves configurations. These instabilities occur in both cases: in the external vertical magnetic field and in the horizontal magnetic field. For all types of instabilities the growth rates are found. In the absence of the vertical magnetic field we obtained the non-linear amplitude equations for the four interacting waves. It is shown that the resulting system of equations has the first integrals that describe the mechanism of energy transfer among interacting waves of small amplitude. This work was supported by the Russian Foundation for Basic Research (project no. 19-02-00016).

How to cite: Klimachkov, D. and Petrosyan, A.: Non-linear waves interactions in rotating shallow water magnetohydrodynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11902, https://doi.org/10.5194/egusphere-egu2020-11902, 2020.

Alpha particles (He⁺⁺) are the most important minor ion species in the solar wind, constituting typically about 5% of the total ion number density. When crossing an interplanetary shock protons and He⁺⁺ particles are accelerated differently due to their different charge-to-mass ratio. This behavior can produce changes in the velocity distribution function (VDF) for both species in the immediate downstream region generating anisotropy in the temperature which is considered to be the energy source for various phenomena such as ion cyclotron and mirror mode waves for example. How these changes in temperature anisotropy and shock structure depend on the percentage of He⁺⁺ particles and the geometry of the shock is not completely understood. In this work we perform various 2D local hybrid simulations (particle ions, massless fluid electrons) with similar characteristics (e.g., Mach number) to observed interplanetary shocks for both quasi-parallel and quasi-perpendicular geometries including self-consistently different percentages of He⁺⁺ particles. We find that the change of the initial θ_Bn leads to variations of the efficiency with which particles can escape to the upstream region facilitating or not the formation of compressive structures in the magnetic field that will produce increments in perpendicular temperature. The regions where both temperature anisotropy and compressive fluctuations appear tend to be more extended and reach higher values as the He⁺⁺ content in the simulations increase.

How to cite: Preisser, L., Blanco-Cano, X., Trotta, D., Burgess, D., and Kajdic, P.: Influence of He++ and shock geometry on interplanetary shocks in the solar wind: 2D Hybrid simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12100, https://doi.org/10.5194/egusphere-egu2020-12100, 2020.

The solar wind in the heliosheath beyond the termination shock (TS) is a non-equilibrium collisionless plasma consisting of thermal solar wind ions, suprathermal pickup ions (PUI) and electrons. In such multi-ion plasma, two fast magnetosonic wave modes exist: the low-frequency fast mode that propagates in the thermal ion component and the high-frequency fast mode that propagates in the suprathermal PUI component [Zieger et al., 2015]. Both fast modes are dispersive on fluid and ion scales, which results in nonlinear dispersive shock waves. In this talk, we briefly review the theory of dispersive shock waves in multi-ion collisionless plasma. We present high-resolution three-fluid simulations of the TS and the heliosheath up to 2.2 AU downstream of the TS. We show that downstream propagating nonlinear magnetosonic waves grow until they steepen into shocklets (thin current sheets), overturn, and start to propagate backward in the frame of the downstream propagating wave, as predicted by theory [McKenzie et al., 1993; Dubinin et al., 2006]. The counter-propagating nonlinear waves result in fast magnetosonic turbulence far downstream of the shock. Since the high-frequency fast mode is positive dispersive on fluid scale, energy is transferred from small scales to large scales (inverse energy cascade). Thermal solar wind ions are preferentially heated by the turbulence. Forward and reverse shocklets in the heliosheath can efficiently accelerate both ions and electrons to high energies through the shock drift acceleration mechanism. We validate our three-fluid simulations with in-situ high-resolution Voyager 2 magnetic field and plasma observations at the TS and in the heliosheath. Our simulations reproduce the magnetic turbulence spectrum with a spectral slope of -5/3 observed by Voyager 2 in frequency domain [Fraternale et al., 2019]. However, since Taylor’s hypothesis is not true for fast magnetosonic perturbations in the heliosheath, the inertial range of the turbulence spectrum is not a Kolmogorov spectrum in wave number domain. 

How to cite: Zieger, B.: Inverse Energy Cascade of Fast Magnetosonic Turbulence in the Heliosheath, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12219, https://doi.org/10.5194/egusphere-egu2020-12219, 2020.

How to cite: Comisel, H., Narita, Y., and Motschmann, U.: Growth rate evaluation for the decay instability in space plasmas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13622, https://doi.org/10.5194/egusphere-egu2020-13622, 2020.

Solar magnetic field is a key paramters to understand the solar activity and its influence to the interplanetary space in the solar system. The solar magnetic field measurement is always an enormous challenge to the solar community. We firstly overview the history of solar magnetic field measurement since last early century and analyze the difficulty and progress of pratical methods. Then we introduce an infrared system for the accurate measurement of solar magnetic field (AIMS) and its current progress, which is supported by National Natural Science Foundation of China and also the current ongoing space based projects (ASO-S/FMG) to measure the solar magnetic field in China.

How to cite: Deng, Y.: Introduction to the current status of solar magnetic field measurements in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13638, https://doi.org/10.5194/egusphere-egu2020-13638, 2020.

In the framework of MHD turbulence, the velocity and magnetic field topological features can be characterized by three quantities invariant under rotations, which are defined by the velocity and magnetic field gradient tensors. These quantities provide information about field structures and dissipative features. 
In this work we present a preliminary derivation of the evolution of the invariant quantities of the velocity and magnetic field gradient tensors in the framework of MHD theory, using a Lagrangian point of view. This work can be considered as a first step useful to characterize and describe the evolution of the fields structures in  heliospheric space plasmas. Furthermore, some examples of the statistical features of magnetic field gradient tensor invariants, in the inertial and dissipation ranges, are also shown and discussed. 

How to cite: Consolini, G., Quattrociocchi, V., Materassi, M., Alberti, T., and Stumpo, M.: On the invariants of velocity and magnetic field gradient tensors in MHD theory, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18602, https://doi.org/10.5194/egusphere-egu2020-18602, 2020.

    Magnetic helicity is conserved in ideal magnetic fluid and is still approximately conserved in the process of fast magnetic reconnection when the magnetic Reynolds number is large enough. We can derive the magnetic helicity injecting into corona from the magnetic helicity flux through photoshpere. A statistical research is carried out to investigate the dissipation of magnetic helicity during the major flares. We choose 69M-up flares from 16 major flare-productive active regions in 24th cycle to research the helicity in corona. Among these flares, 19 is X-up flares. We utilize Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) and 12-min successive vector magnetograms from Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to derive the flux of magnetic helicity through photosphere. At the same time, we extrapolate the vector magnetic field in corona to calculate the relative helicity by the suppose of Non-linear Force Free Field (NLFFF). The calculation window is 12-18 minutes before and after flares. A well correlation is shown between the magnetic free energy and magnetic helicity, the threshold of triggering M-up flare is the change of magnetic helicity above 2×10⁴²Mx² and the change of magnetic free energy above 3 × 10³¹erg . Considering one fifth of magnetic helicity injecting into corona, the dissipation of magnetic helicity during the flares is 6-7 % , which is corresponding to the result of previous numerical simulation results, which strongly support that the magnetic helicity is approximate conserved during the major flares.

How to cite: Wang, Q., Yang, S., Zhang, M., and Wiegelmann, T.: Relative magnetic helicity dissipation during the major flares, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18835, https://doi.org/10.5194/egusphere-egu2020-18835, 2020.

The characteristic relaxation time of the Uranus magnetosphere is of the order  of the planet's rotation period. This is also the case for Jupiter or Saturn. However, the specificity of Uranus (and to a lesser extent of  Neptune) is that the rotation axis and the magnetic dipole axis are separated by  a large angle (~60°) the consequence of which is the development of a highly dynamic and complex magnetospheric tail. In addition, and contrary to all other planets of the solar system, the rotation axis of Uranus happens to be quasi-parallel to the ecliptic plane which also implies a strong variability of the magnetospheric structure as a function of the season. The magnetosphere of Uranus is thus a particularly challenging case for global plasma simulations, even in the frame of MHD. We present MHD simulations of a Uranus type magnetosphere at both equinox (solar wind is orthogonal to the planetary rotation axis) and solstice (solar wind is orthogonal to the planetary rotation axis) configurations. The main differences between the two configurations will be discussed. 

How to cite: Pantellini, F. and Griton, L.: MHD simulations of an Uranus type rotating magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18905, https://doi.org/10.5194/egusphere-egu2020-18905, 2020.

According to Helios, Ulysses, New Horizons measurements at a wide range of distances from the Sun, radial evolution of solar wind ion temperature significantly deviates from the adiabatic expansion model:  additional heating of the solar wind plasma is required to describe observational data. Solution of the solar wind heating problem is extremely important both for understanding the structure of the heliosphere and for adequately describing the atmospheres of distant stars. Solar wind magnetic field is turbulent and this turbulence is dominated by numerous small-scale high-amplitude coherent structures – such as quasi-1D discontinuities. Modern theoretical models predict that quasi-1D discontinuities can play important role in solar wind heating. We collected the statistics of MMS observations of thin quasi-1D discontinuities in the solar wind to reveal their characteristics. Analyzing observational data, we construct the discontinuity model and use it to consider non-adiabatic interaction of ions with solar wind discontinuities. We mainly focus on discontinuity roles in solar wind ion scattering and thermalization. This presentation shows how discontinuity configuration affects the scattering rates.

How to cite: Vinogradov, A., Artemyev, A., Vasko, I., Vasiliev, A., and Petrukovich, A.: Non-adiabatic interaction of ions with solar wind discontinuities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20301, https://doi.org/10.5194/egusphere-egu2020-20301, 2020.

Electron temperature anisotropy instabilities are believed to constrain the distributions of the electron parallel and perpendicular temperatures in the solar wind. When the electron perpendicular temperature is larger than the parallel temperature, the whistler instability is normally stronger than the electron mirror instability. While the electron parallel temperature is larger than the perpendicular temperature, the electron oblique firehose instability dominates the parallel firehose instability. Therefore, previous studies proposed the whistler and electron oblique firehose instabilities constraint on the electron dynamics in the solar wind. Based on the fact that there always exists the differential drift velocity among different electron populations, we consider the electron kinetic instability in the plasmas containing the electron anisotropic component and the electron beam component. Consequently, we give a comprehensive electron kinetic instability analysis in the solar wind. Furthermore, we propose that the electron acoustic/magneto-acoustic instability can arise in the low electron beta regime, and the whistler electron beam instability can be triggered in a wide beta regime. These two instabilities can provide a constraint on the electron beam velocity. Moreover, we find a new instability in the regime of the electron beta ~ 1, and this instability produces obliquely-propagating fast-magnetosonic/whistler waves. These results would be helpful for distinguishing the electron instability and for analyzing the constraint mechanism on the electron temperature distribution in the solar wind.

How to cite: Zhao, J., Sun, H., Liu, W., Xie, H., and Wu, D.: Electron Kinetic Instability Driven by Electron Temperature Anisotropy and Electron Beam in the Solar Wind, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21114, https://doi.org/10.5194/egusphere-egu2020-21114, 2020.