NP6.1

Shock waves in collisionless plasmas are common in heliospheric and astrophysical settings and are some of the most efficient particle accelerators in space. Shocks can undergo self-reformation where a new shock front appears in front of the previous shock front. Shock reformation has been observed previously in both spacecraft observations and simulations, but the process is not yet fully understood. We here study self-reformation of Earth's quasi-parallel bow shock with observations from the four MMS spacecraft and simulation results from the hybrid-Vlasov simulation Vlasiator. We find, in both observations and simulation, that short large amplitude magnetic structures (SLAMS) can constitute shock reformation. The SLAMS form upstream of the shock and grow in amplitude while being convected towards the shock and eventually forming the new shock front. Using MMS's and Vlasiator's high-cadence field and ion measurements, we study how the shock reformation process influences the dynamics and acceleration of ions at the quasi-parallel shock.

How to cite: Johlander, A., Battarbee, M., Turc, L., Pfau-Kempf, Y., Ganse, U., Grandin, M., Dubart, M., Alho, M., Bussov, M., George, H., Tarvus, V., Papadakis, K., Suni, J., Zhou, H., and Palmroth, M.: Magnetic structures and reformation at quasi-parallel shocks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14776, https://doi.org/10.5194/egusphere-egu21-14776, 2021.

Energy dissipation at collisionless shocks is still an open question. Wave particle interactions are believed to be at the heart of it, but the exact details are still to be figured out. One type of waves that is known to be an efficient dissipator of solar wind kinetic energy are electrostatic waves in the shock ramp, such as ion acoustic waves with frequency around the ion plasma frequency or Bernstein waves with frequency around the electron cyclotron frequency and its harmonics. The electric field of such waves is typically larger than 100 mV/m, large enough to disturb particle dynamics. In this study we use the magnetospheric multiscale (MMS) spacecraft, to investigate the source and evolution of electrostatic waves in the shock ramp of quasi-perpendicular super-critical shocks, and study their effect on solar wind thermalization.

How to cite: Lalti, A., Khotyaintsev, Y., Graham, D., Vaivad, A., and Johlander, A.: Electrostatic waves in the shock ramp and their effect on plasma energetics., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14805, https://doi.org/10.5194/egusphere-egu21-14805, 2021.

Electric fields (E) play a fundamental role in facilitating the exchange of energy between the electromagnetic fields and the changed particles within a plasma. Decomposing E into the contributions from the different terms in generalized Ohm's law, therefore, provides key insight into both the nonlinear and dissipative dynamics across the full range of scales within a plasma. Using the unique, high‐resolution, multi‐spacecraft measurements of three intervals in Earth's magnetosheath from the Magnetospheric Multiscale mission, the influence of the magnetohydrodynamic, Hall, electron pressure, and electron inertia terms from Ohm's law, as well as the impact of a finite electron mass, on the turbulent electric field spectrum are examined observationally for the first time. The magnetohydrodynamic, Hall, and electron pressure terms are the dominant contributions to E over the accessible length scales, which extend to scales smaller than the electron gyroradius at the greatest extent, with the Hall and electron pressure terms dominating at sub‐ion scales. The strength of the non‐ideal electron pressure contribution is stronger than expected from linear kinetic Alfvén waves and a partial anti‐alignment with the Hall electric field is present, linked to the relative importance of electron diamagnetic currents within the turbulence. The relative contributions of linear and nonlinear electric fields scale with the turbulent fluctuation amplitude, with nonlinear contributions playing the dominant role in shaping E for the intervals examined in this study. Overall, the sum of the Ohm's law terms and measured E agree to within ∼ 20% across the observable scales. The results both confirm a number of general expectations about the behavior of E within turbulent plasmas, as well as highlight additional features that may help to disentangle the complex dynamics of turbulent plasmas and should be explored further theoretically.

How to cite: Stawarz, J., Matteini, L., Parashar, T., Franci, L., Eastwood, J., Gonzalez, C., Gingell, I., Burch, J., Ergun, R., Ahmadi, N., Giles, B., Gershman, D., Le Contel, O., Lindqvist, P.-A., Russell, C., Strangeway, R., and Torbert, R.: Comparative Analysis of the Various Generalized Ohm's Law Terms in Magnetosheath Turbulence as Observed by Magnetospheric Multiscale, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6249, https://doi.org/10.5194/egusphere-egu21-6249, 2021.

Shocks and turbulence are spectacular, ubiquitous phenomena and are crucial ingredients to understand the production and transport of energetic particles in several astrophysical systems. The interaction between an oblique, supercritical shock and fully developed plasma turbulence is here investigated by means of kinetic simulations, for different turbulence amplitudes. The role of pre-existing, upstream turbulence on plasma transport is addressed using a novel technique, relying on the coarse-graining of the Vlasov equation. We find that the upstream transport properties strongly depend on upstream turbulence strength, with patterns modulated by the presence of turbulent structures. These results are relevant for a variety of systems, ranging from the Earth's bow shock interacting with solar wind turbulence, to the largest scales of radio relics in galaxy clusters.

How to cite: Trotta, D., Valentini, F., Burgess, D., and Servidio, S.: Particle energisation and transport at collisionless shocks propagating through turbulent media., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12451, https://doi.org/10.5194/egusphere-egu21-12451, 2021.

The propagation of collisionless shocks through the turbulent magnetized plasmas has been investigated for decades. The processes connected with the formation and propagation of Interplanetary (IP) shocks play a key role in the acceleration of particles and in the coupling to the Earth’s magnetosphere. However, many aspects of the interactions are poorly understood, e.g., the regime of turbulence in downstream/upstream medium, heating of the downstream plasma via turbulent dissipation, etc. Recently, a few authors have addressed the nature of fluctuations within the downstream regions of IP shocks and sheaths of ICMEs. In general, they have found that an IP shock enhances the fluctuation energy within the downstream plasma. Consequently, this should lead to the enhanced heating of the shocked plasma. In this study, we investigate whether the downstream region exhibits such a heating. In the analysis, we stress that the downstream region (in situ observation by a spacecraft) of an IP shock is an evolutionary record of the shocked plasma, i.e., the leading edge of a sheath is plasma that has been just shocked, while the plasma recorded 1 hour after the shock passage has been shocked roughly 5–6 hours earlier, on average. We illustrate this point investigating the relation of the enhanced levels of turbulent fluctuations by the IP shocks and the temperature evolution in the downstream plasma. Preliminary results suggest that the level of enhanced fluctuations affects the temperature profile in this region.

How to cite: Pitna, A., Šafránková, J., and Němeček, Z.: On the interaction of interplanetary shocks and solar wind turbulence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2853, https://doi.org/10.5194/egusphere-egu21-2853, 2021.

We investigate the properties of an interplanetary shock (M_A=3.0, θ_Bn=80°) propagating in Super-Alfvénic solar wind observed on September 12^th, 1999 with in situ Wind/MFI and Wind/3DP observations. Key results are obtained concerning the possible energy dissipation mechanisms across the shock and how the shock modifies the ambient solar wind at MHD and kinetic scales:  (1) Waves observed in the far upstream of the shock are incompressional and mostly shear Alfvén waves.  (2) In the downstream, the shocked solar wind shows both Alfvénic and mirror-mode features due to the coupling between the Alfvén waves and ion mirror-mode waves.  (3) Specularly reflected gyrating ions, whistler waves, and ion cyclotron waves are observed around the shock ramp, indicating that the shock may rely on both particle reflection and wave-particle interactions for energy dissipation.  (4) Both ion cyclotron and mirror mode instabilities may be excited in the downstream of the shock since the proton temperature anisotropy touches their thresholds due to the enhanced proton temperature anisotropy.  (5) Whistler heat flux instabilities excited around the shock give free energy for the whistler precursors, which help explain the isotropic electron number and energy flux together with the normal betatron acceleration of electrons across the shock.  (6) The shock may be somehow connected to the electron foreshock region of the Earth’s bow shock, since Bx > 0, By < 0, and the electron flux varies only when the electron pitch angles are less than PA = 90°, which should be further investigated. Furthermore, the interaction between Alfvén waves and the shock and how the shock modifies the properties of the Alfvén waves are also discussed.

How to cite: Liu, M., Yang, Z., Liu, Y. D., Lembege, B., Issautier, K., Wilson III, L. B., Zhao, S., Jagarlamudi, V. K., and Zhao, X.: Properties of A Supercritical Quasi-Perpendicular Interplanetary Shock Propagating in Super-Alfvénic Solar Wind: from MHD to Kinetic Scales, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4908, https://doi.org/10.5194/egusphere-egu21-4908, 2021.

Microinstabilities and waves excited at perpendicular interplanetary shocks in the near-Sun solar wind are investigated by full particle-in-cell simulations. By analyzing the dispersion relation of fluctuating field components directly issued from the shock simulation, we obtain key findings concerning wave excitations at the shock front: (1) at the leading edge of the foot, two types of electrostatic (ES) waves are observed. The relative drift of the reflected ions versus the electrons triggers an electron cyclotron drift instability (ECDI) that excites the first ES wave. Because the bulk velocity of gyro-reflected ions shifts to the direction of the shock front, the resulting ES wave propagates obliquely to the shock normal. Immediately, a fraction of incident electrons are accelerated by this ES wave and a ring-like velocity distribution is generated. They can couple with the hot Maxwellian core and excite the second ES wave around the upper hybrid frequency. (2) From the middle of the foot all the way to the ramp, electrons can couple with both incident and reflected ions. ES waves excited by ECDI in different directions propagate across each other. Electromagnetic (EM) waves (X mode) emitted toward upstream are observed in both regions. They are probably induced by a small fraction of relativistic electrons. The impact of shock front rippling, Mach numbers, and dimensions on the ES wave excitation also will be discussed. Results shed new insight on the mechanism for the occurrence of ES wave excitations and possible EM wave emissions at young coronal mass ejection–driven shocks in the near-Sun solar wind.

How to cite: Yang, Z., Matsukiyo, S., Xie, H., Guo, F., Liu, M., Gao, X., Lu, Q., and Wang, C.: Microinstabilities and plasma waves at Near-Sun Solar Wind collisionless Shocks: Predictions for PSP and SO, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8114, https://doi.org/10.5194/egusphere-egu21-8114, 2021.

In our study we analyzing the fine structure of interplanetary shock wave fronts recorded by the BMSW experiment, installed onboard the SPEKTR-R satellite. The high time resolution of the spectrometer (0.031 s for the plasma flux magnitude and direction and 1.5 s for velocity, temperature, and density) makes it possible to study the internal structure of the IPs front.

BMSW experiment registered 55 IPs waves from 2011 to 2019. For 21 events (where the temperature was not very high), the parameters of twice-ionized helium (He++ or α-particles) - density (absolute value and relative to protons content in the solar wind plasma), velocity, temperature. It is shown that the speed of He++ is slightly less (for about 5%) than the speed of protons, the relative density of He++ rarely exceeds 10%, and the temperature of He++ is about 2 times higher than the temperature of protons.

On the IPs front, short-term and significant (up to 20%) jumps in the relative density of He++ were detected in several events. No dependence was found between Mms/proton beta and He++ density changing after IPs front. However, we detected that the lower Qbn parameter is, the more the relative density of He++ falls behind the IPs front.

How to cite: Sapunova, O., Borodkova, N., Yermolaev, Y., and Zastenker, G.: He++  behavior on the an interplanetary shock wave, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6073, https://doi.org/10.5194/egusphere-egu21-6073, 2021.

The structure of quasiperpendicular interplanetary (IP) shock fronts was studied based on the data from the BMSW plasma spectrometer, installed onboard the SPEKTR-R spacecraft, supplemented by magnetic field measurements on the WIND. Special attention was paid to periodic growths (overshoots) in the value of the ion flux relative to their mean values outside the ramp. A comparison of plasma overshoot was performed with the overshoot in the magnetic field, with the Mach number, and with the β parameter. Based on the analysis of 26 crossings of IP shocks, in which the overshoots in the ion flux and magnetic field value were observed, it was shown that the value of the magnetic field overshoot is, on the average, less than a similar value in the solar wind’s ion flux, which is associated with different time resolution of measurements.

The ion flux overshoot value is found to grow with the growth of the Mach number. It is shown that overshoots are formed not only in the supercritical shocks, but also in those with Mach numbers that are less than the value of the first critical Mach number. It is also found that the estimates of the coherent downstream oscillations of the ion flux and magnetic field good correlate with the convected ion gyroradius.

This work was supported by the Russian Foundation for Basic Research, grant no. 19-02-00177.

How to cite: Borodkova, N., Sapunova, O., Eselevich, V., Zastenker, G., and Yermolaev, Y.: Comparison of Plasma and Magnetic Overshoots of Interplanetary Shocks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10163, https://doi.org/10.5194/egusphere-egu21-10163, 2021.

 The chromospheric heating problem is a long-standing intriguing topic of solar physics, and the acoustic wave/shock wave heating in the chromospheric plasma has been investigated in the last several decades. It has been confirmed that acoustic waves, and the shock waves induced by the steepening acoustic waves in the gravitationally stratified chromospheric plasma, are able to transport energy to the chromosphere, but the energy supplied in this way is not necessarily sufficient for heating the chromosphere. Here, we further investigate the acoustic/shock wave heating process while taking into account the two-fluid effects.

 As the plasma in the chromosphere is weakly or partially ionized,  neutrals play an important role in wave propagation in this region. Therefore,  a two-fluid computational model treating neutrals and charged particles (electrons and ions) as two separate fluids is used for modelling the acoustic/shock wave propagation in idealised partially ionized plasmas, while taking into account the ion-neutral collisions, ionization and recombination. We have thus investigated  the collisional and reactive interactions between separated ions and neutrals, as well as the resulting effects in the acoustic/shock wave propagation and damping. In the numerical simulations, both the initial hydrostatic equilibrium and chemical equilibrium are taken into account to provide different density profiles for comparison.

We have found that the shock heating in the partially ionized plasmas strongly depends on the ionization fraction. In particular, the relatively smaller ionization fraction resulting from the initial chemical equilibrium significantly enhances the shock wave heating, which dominates the overall heating effect according to an approximated quantitative comparison. Moreover, the decoupling between ions and neutrals is also enhanced while considering ionization and recombination, resulting in stronger collisional heating.

How to cite: Zhang, F., Poedts, S., Lani, A., Kuźma, B., and Murawski, K.: Acoustic/shock wave heating in the gravitationally stratified partially ionized plasmas: the two-fluid effects, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10359, https://doi.org/10.5194/egusphere-egu21-10359, 2021.

The purpose of our study is to deepen our understanding on the turbulence that arises from Rayleigh Taylor Instabilities in quiescent solar prominences. Quiescent prominences in the solar corona are cool and dense condensates that show internal dynamics over a wide range of spatial and temporal scales. These dynamics are dominated by vertical flows in the prominence body where the mean magnetic field is predominantly in the horizontal direction and the magnetic pressure suspends the dense prominence material. We perform numerical simulations using  MPI-AMRVAC (http://amrvac.org) to study the Rayleigh Taylor Instabilitiy at the prominence-corona transition region using the Ideal-magentohydrodyamics approach. High resolution simulations achieve a resolution of ∼23 km for ∼21 min transitioning from a multi-mode perturbation instability to the non-linear regime and finally a fully turbulent prominence. We use statistical methods to quantify the rich dynamics in quiescent prominence as being indicative of turbulence.

How to cite: Changmai, M. and Keppens, R.: Turbulence characteristics of Solar Prominences due to Rayleigh Taylor Instabilities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11979, https://doi.org/10.5194/egusphere-egu21-11979, 2021.

The physical foundations of the dissipation of energy and the associated heating in weakly collisional plasmas are poorly understood. Here, we compare and contrast several measures that have been used to characterize energy dissipation and kinetic-scale conversion in plasmas by means of a suite of kinetic numerical simulations describing both magnetic reconnection and decaying plasma turbulence. We adopt three different numerical codes that can also include inter-particle collisions: the fully-kinetic particle-in-cell vpic, the fully-kinetic continuum Gkeyll, and the Eulerian Hybrid Vlasov-Maxwell (HVM) code. We differentiate between i) four energy-based parameters, whose definition is related to energy transfer in a fluid description of a plasma, and ii) four distribution function-based parameters, requiring knowledge of the particle velocity distribution function. There is overall agreement between the dissipation measures obtained in the PIC and continuum reconnection simulations, with slight differences due to the presence/absence of secondary islands in the two simulations. There are also many qualitative similarities between the signatures in the reconnection simulations and the self-consistent current sheets that form in turbulence, although the latter exhibits significant variations compared to the reconnection results. All the parameters confirm that dissipation occurs close to regions of intense magnetic stresses, thus exhibiting local correlation. The distribution function-based measures show a broader width compared to energy-based proxies, suggesting that energy transfer is co-localized at coherent structures, but can affect the particle distribution function in wider regions. The effect of inter-particle collisions on these parameters is finally discussed.

How to cite: Cassak, P., Pezzi, O., Liang, H., Juno, J., Vasconez, C., Sorriso-Valvo, L., Perrone, D., Servidio, S., Roytershteyn, V., TenBarge, J., and Matthaeus, W.: Dissipation measures in weakly-collisional plasmas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3210, https://doi.org/10.5194/egusphere-egu21-3210, 2021.

The understanding of magnetic reconnection's physical processes has considerably been improved thanks to the data of the Magnetopsheric Multiscale mission (MMS). However, a lot of work still has to be done to better characterize the core of the reconnection process : the electron diffusion region (EDR). We previously developed a machine learning algorithm to automatically detect EDR candidates, in order to increase the available list of events identified in the literature. However, identifying the parameters that are the most relevant to describe EDRs is complex, all the more that some of the small scale plasma/fields parameters show limitations in some configurations such as for low particle densities or large guide fields cases. In this study, we perform a statistical study of previously reported dayside EDRs as well as newly reported EDR candidates found using machine learning methods. We also show different single and multi-spacecraft parameters that can be used to better identify dayside EDRs in time series from MMS data recorded at the magnetopause. And finally we show an analysis of the link between the guide field and the strength of the energy conversion around each EDR.

How to cite: Lenouvel, Q., Génot, V., Garnier, P., Lavraud, B., and Toledo, S.: EDR signatures observed by MMS : a statistical study of dayside events found with machine learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2381, https://doi.org/10.5194/egusphere-egu21-2381, 2021.

The formation of coherent current structures in turbulent collisionless magnetized plasmas and their disruption through magnetic reconnection has been extensively studied in past years via in situ observations, numerical simulations, and theoretical models. Presently there is no automatic verified way to detect reconnection events so that only an accurate human analysis can be performed. We set-up a machine learning unsupervised technique aimed at automatically detecting the presence of current sheet (CS) magnetic structures where reconnection is occurring. We make use of clustering techniques as KMeans and DBscan, and compare their efficiency to that of simpler methods which do not use machine learning but are only based on thresholds on important physical quantities. The unsupervised machine learning method turns out to be the one with the best performance. We applied these techniques to 2D kinetic HVM (Hybrid Vlasov Maxwell) plasma turbulence simulations, where ions evolve by solving the Vlasov equation while the electrons are treated as a fluid. Electron inertia is included. We are presently working on adapting our techniques to 1D time series extracted from our simulations aiming at reproducing typical data measured by satellites. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 776262 (AIDA, www.aida-space.eu).

How to cite: Sisti, M., Finelli, F., Pedrazzi, G., Faganello, M., Califano, F., Delli Ponti, F., and Zalizniak, V.: Using clustering techniques for magnetic reconnection detection, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2659, https://doi.org/10.5194/egusphere-egu21-2659, 2021.

In space and astrophysical plasmas magnetized coherent structures continuously emerge as an outcome of the nonlinear dynamics. These structures are characterized  by the presence of localized strong current density peaks. Here we present a statistical study of the development of such structures resulting in different hybrid-Vlasov 3D-3V simulations of plasma turbulence. In particular, we make use of different methods to characterize the global shape of the 3D structures. Furthermore, we study the local magnetic configuration inside and outside current peak regions, comparing the statistics in the two cases. Finally, we discuss correlations between characteristic dimensions of the current structures and current density, marking the difference between magnetic structures in 2D and 3D simulations.

How to cite: Faganello, M., Sisti, M., Fadanelli, S., Cerri, S. S., Califano, F., and Agullo, O.: Investigating current structures in 3D-3V hybrid Vlasov simulations of turbulence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2744, https://doi.org/10.5194/egusphere-egu21-2744, 2021.

Heating and energy dissipation in the solar wind remain important open questions. Turbulence and reconnection are two candidate processes to account for the energy transport to subproton scales at which, in collisionless plasmas, the energy ultimately dissipates. Understanding the effects of small-scale reconnection events in the energy cascade requires the identification of these events in observational data as well as in 3D simulations. We use an explicit fully kinetic particle-in-cell code to simulate 3D small scale magnetic reconnection events forming in anisotropic and Alfvénic decaying turbulence. We define a set of indicators to find reconnection sites in our simulation based on intensity thresholds.  According to the application of these indicators, we identify the occurrence of reconnection events in the simulation domain and analyse one of these events in detail. The event is highly dynamic and asymmetric. We study the profiles of plasma and magnetic-field fluctuations recorded along artificial-spacecraft trajectories passing near and through the reconnection region as well as the energy exchange between particles and fields during this event. Our results suggest the presence of particle heating and acceleration related to asymmetric small-scale reconnection of magnetic flux tubes produced by the anisotropic Alfvénic turbulent cascade in the solar wind. These events are related to current structures of order a few ion inertial lengths in size.

How to cite: Agudelo Rueda, J. A., Verscharen, D., Wicks, R. T., Owen, C. J., Nicolaou, G., Walsh, A. P., Zouganelis, Y., Germaschewski, K., and Vargas-Dominguez, S.: Energy transport during 3D small-scale reconnection driven by anisotropic turbulence using PIC simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8544, https://doi.org/10.5194/egusphere-egu21-8544, 2021.

There are many fundamental questions about the temporal and spatial structure of turbulence in space plasmas. Answering these questions is complicated by the multi-scale nature of the turbulent transfer of mass, momentum, and energy, with characteristic scales spanning many orders of magnitude. The solar wind is an ideal environment in which to measure turbulence, but multi-point observations with spacecraft separations spanning these scales are needed to simultaneously characterize structure and cross-scale couplings. In this work, we use synthetic multi-point spacecraft data extracted from numerical simulations to demonstrate the utility of multi-point, multi-scale measurements, in preparation for data from future multi-spacecraft observatories. We use the baseline orbit design for the HelioSwarm mission concept to explore the effects of different inter-spacecraft separations and geometries on the accuracy of reconstructed magnetic fields, cascade rates, and correlation functions using well-established analysis techniques.

How to cite: Klein, K. and Spence, H. and the HelioSwarm Science Team: HelioSwarm: Leveraging Multi-Point, Multi-Scale Spacecraft Observations to Characterize Turbulence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6812, https://doi.org/10.5194/egusphere-egu21-6812, 2021.

The electromagnetic branch of the lower-hybrid drift instability (LHDI) can lead to kinking of current sheets and fluctuations in the magnetic field and is present for example in Earth’s magnetosphere. Previous particle-in-cell studies suggested that the electromagnetic LHDI’s saturation is at a moderate level and that strong current sheet kinking is only caused by slower kink-type modes. Here, we present kinetic continuum simulations that show strong kinking and high saturation levels of the B-field fluctuations. Has the impact of the electromagnetic LHDI been underestimated? The capability of the LHDI to produce x-lines and turbulence in 3D reconnection is discussed at the example of ten-moment multi-fluid simulations.

How to cite: Allmann-Rahn, F., Lautenbach, S., Sydora, R., and Grauer, R.: Strong B-Field Fluctuations Caused by the Electromagnetic LHDI and their Impact on 3D Reconnection, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9637, https://doi.org/10.5194/egusphere-egu21-9637, 2021.

Plasma waves and instabilities driven by temperature anisotropies are known to play a significant role in plasma dynamics, scattering the particles and affecting particle heating and energy conversion between the electromagnetic fields and the particles. Among these instabilities, the electron firehose instability is driven by electron temperature anisotropy T_e, > T_e,perp (with respect to the background magnetic field) and produce nonpropagating oblique modes. 

Magnetic reconnection is characterized by regions of enhanced temperature anisotropy that could drive instabilities - including the electron firehose instability - affecting the particle dynamics and the energy conversion of the process. Yet, the electron firehose instability and its role in the reconnection process is still rather unexplored, especially with in situ measurements. 

We report MMS observations of electron firehose fluctuations observed in the exhaust region of a reconnection site in the magnetotail. The fluctuations are observed in the Earthward outflow relatively close (less than 2 d_i distance) to the electron diffusion region (EDR). While the characteristics of the fluctuations are compatible with oblique electron firehose fluctuations, the associated firehose instability threshold is not exceeded in the interval where the fluctuations are observed. However, the threshold is exceeded in the EDR. The wave analysis in the EDR suggests that the firehose instability could be active at the reconnection site. We suggest that the firehose fluctuations observed in the outflow region may have been originated at the EDR, where the electron temperature anisotropy exceeds the threshold values, and then advected in the outflow region.

How to cite: Cozzani, G., Khotyaintsev, Y., Graham, D., and André, M.: MMS observations of electron firehose fluctuations in the magnetic reconnection outflow, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14401, https://doi.org/10.5194/egusphere-egu21-14401, 2021.

Kelvin-Helmholtz instability is a widespread phenomenon in space plasmas, such as at the planetary magnetospheres. During its nonlinear phase, the generation of Kelvin-Helmholtz vortices takes place. The identification of such coherent structures is not straightforward in observational data contrary to numerical simulations where both temporal evolution and spatial behavior can be observed. Recently, a comparison between a hybrid Vlasov-Maxwell simulation and Magnetospheric Multi-Scale satellites observation of a Kelvin-Helmholtz event has shown the presence of kinetic features that can uniquely characterize the boundaries of Kelvin-Helmholtz vortices.  Indeed, a strong total current density has been observed in correspondence of the edges of each vortex associated with a weakly distorted distribution function from the equilibrium distribution; while the opposite occurs inside the vortex region. Moreover, a new tool has been proposed to distinguish the different phases of the Kelvin-Helmholtz instability and to identify the trajectory of the spacecraft across the vortex itself. Such a tool takes into consideration the mixing degree between the magnetospheric-like and magnetosheath-like particles population in the Earth environment. The clear identification of a vortex in in situ data is an important achievement since it can provide a better understanding of the role that Kelvin-Helmholtz instability plays in weakly collisional space plasmas in the contest of energy dissipation.

This work has received funding from the European Unions Horizon 2020 research and innovation programme under grant agreement no. 776262 (AIDA,).

How to cite: Settino, A., Perrone, D., Khotyaintsev, Y. V., Graham, D. B., Pezzi, O., Malara, F., and Valentini, F.: Identification of Kelvin-Helmholtz vortices at the Earth’s magnetosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9912, https://doi.org/10.5194/egusphere-egu21-9912, 2021.

Magnetic reconnexion and Kelvin-Helmholtz (KH) instability are usually recognized as the two main mixing processes along magnetopauses. However, a recent work [Dargent et al., 2019] showed that in Mercury’s conditions, another instability can grow faster than the KH instability along the magnetopause. This instability seems to rely on gradients of density and/or magnetic field and develops large-scales finger-like structures that prevents the growth of the KH vortices. In this work, I will characterize this instability and try to identify it. In particular, I will look at the dependance of the growth rate of this instability to the different parameters of the plasma and compare it to the growth rate of the Kelvin-Helmholtz instability.

How to cite: Dargent, J., Lavorenti, F., Henri, P., and Califano, F.: A large-scale instability competing with Kelvin-Helmholtz at Mercury’s boundary layer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9413, https://doi.org/10.5194/egusphere-egu21-9413, 2021.

Already several decades ago, it was suggested that kinetic instabilities play a fundamental role in heat flux regulation at relatively large distances from the Sun, R> 1 AU [Scime et al, 1994]. Now, Parker Solar Probe observations have established that this is the case also closer to it [Halekas et al, 2020].

Electron scale instabilities in the solar wind are driven and affected in their evolution by the slow, large scale process of solar wind expansion, as demonstrated observationally [Stverak et al, 2008; Bercic et al, 2020], and via fully kinetic Expanding Box Model simulations [Innocenti et al, 2019b].

Now, connecting the dots, we examine an indirect role of plasma expansion in heat flux regulation in the solar wind. We show, as a proof of principle, that plasma expansion can modify heat flux evolution as a function of heliocentric distance, with respect to what is expected within an adiabatic framework, due to the onset of kinetic instabilities, in this case, an oblique firehose instability developing self consistently in the presence of a core and suprathermal electron population [Innocenti et al, 2020].

This result highlights, once again, the deeply multi scale nature of the heliospheric environment, that calls for advanced simulation techniques. In this work, the simulations are done with the fully kinetic, semi-implicit [Markidis et al, 2010], Expanding Box Model [Velli et al, 1992] code EB-iPic3D [Innocenti et al, 2019a].

How to cite: Innocenti, M. E., Boella, E., Tenerani, A., and Velli, M.: A two-step role for plasma expansion in solar wind heat flux regulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6439, https://doi.org/10.5194/egusphere-egu21-6439, 2021.

Electron velocity distribution functions, initially composed of core and strahl populations as typically encountered in the near-Sun solar wind and as recently observed by Parker Solar Probe, have been modeled via fully kinetic Particle-In-Cell simulations. It has been demonstrated that, as a consequence of the evolution of the electron velocity distribution function, two branches of the whistler heat flux instability can be excited, which can drive whistler waves propagating in the direction parallel or oblique to the background magnetic field. First, the strahl undergoes pitch-angle scattering with oblique whistler waves, which provokes the reduction of the strahl drift velocity and the simultaneous broadening of its pitch angle distribution. Moreover, the interaction with the oblique whistler waves results in the scattering towards higher perpendicular velocities of resonant strahl electrons and in the appearance of a suprathermal halo population which, at higher energies, deviates from the Maxwellian distribution. Later on, the excited whistler waves shift towards smaller angles of propagation and secondary scattering processes with quasi-parallel whistler waves lead to a redistribution of the scattered particles into a more symmetric halo. All processes are accompanied by a significant decrease of the heat flux carried by the strahl population along the magnetic field direction, although the strongest heat flux rate decrease is simultaneous with the propagation of the oblique whistler waves.

How to cite: Micera, A., Zhukov, A., López, R. A., Innocenti, M. E., Lazar, M., Boella, E., and Lapenta, G.: Particle-In-Cell simulations of resonant interactions between whistler waves and electrons in the near-Sun solar wind: scattering of the strahl into the halo and heat flux regulation., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10198, https://doi.org/10.5194/egusphere-egu21-10198, 2021.

In order to efficiently convert AW energy into particle energy, the original fluctuation must decay from the initial macroscopic (fluid) scales to smaller (kinetic) scales. This decay can be promoted by the interaction of counter-propagating AWs or by the interaction between AWs and an inhomogeneous background. It has been shown that AWs interacting with an inhomogeneous background can cascade to smaller scales via the phase-mixing process [1]. When the cascade reaches scales comparable with the ion Larmor radius, AWs can efficiently be converted into ”kinetic” Alfvén  waves (KAWs), which represent the natural extension of AWs in the kinetic branch of the wave dispersion relation for wavevectors nearly perpendicular to the background magnetic field [2]. In this work we present the results of a numerical experiment in which the decay of AWs into KAWs is studied self-consistently in a range that goes from fluid to kinetic electron scales. We show how the AW-to-KAW transition, promoted by an inhomogeneous background, leads to the heating of both ions and electrons via two different physical mechanisms. Both mechanisms are illustrated via a simple argument on how the two species can access the kinetic and magnetic energy carried by AWs. Our findings are supported by in-situ observations of KAWs in the Earth’s magnetosphere [3].

[1]  J. Heyvaerts  and  E.  Priest,  Coronal  heating  by  phase-mixed shear Alfv ́en waves, Astronomy and Astrophysics117, 220 (1983).
[2]  J. Hollweg, Kinetic Alfv ́en wave revisited, Journal of Geo-physical Research:  Space Physics104, 14811 (1999)
[3] D. Gershman, F. Adolfo, J. Dorelli, S. Boardsen, L. Avanov, P. Bellan, S. Schwartz, B. Lavraud, V. Cof-fey, M. Chandler,et  al., Wave-particle energy exchangedirectly observed in a kinetic Alfv ́en-branch wave, Naturecommunications8, 1 (2017).

How to cite: Pucci, F., Bacchini, F., Lapenta, G., and Malara, F.: Ion and electron energization by Alfvén waves in magnetic shears, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2955, https://doi.org/10.5194/egusphere-egu21-2955, 2021.