ST1.7

Energetic electrons in impulsive events can serve as an ideal probe of solar wind magnetic field. Using a recently developed Fractonal Velocity Dispersion Analysis (FVDA), the release time at the Sun and the path length of interplanetary magnetic field can be obtained with very small uncertainties in many impulsive events. Further knowing the source location, one can examine how much do the field lines deviate from the Parker spiral.  In this work, we present an analytic model for the angular dispersion of magnetic field lines that results from the turbulence in the solar wind and at the solar source surface. The heliospheric magnetic field lines in this  model is derived from a Hamiltonian $H_{\rm m}(\mu, \phi, r)$ in which the pair of canonically conjugated variables the cosine of the heliographic colatitude $\mu$ and the longitude $\phi$. This model naturally incorporates the effect of a random footpoint motion on the source surface since such a motion is due to the zero-frequency component of the solar wind turbulence. Assuming the footpoint motion is also diffusive, it is shown that the angular diffusivity of the stochastic Parker spirals is given by the angular diffusivity of the footpoints divided by the solar wind speed and is controlled by a unique parameter which is the Kubo number. We also present some model calculations of meandering field lines resulting from stochastic footpoint motion and statistical results of the field line path length from observations. Our model and statistical results can shed lights on observations made by Parker Solar Probe and Solar Orbiter.

How to cite: Li, G., Bian, N., and Zhao, L.: A stochastic solar wind magnetic field model and probing its meandering nature by Energetic Electrons, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-368, https://doi.org/10.5194/egusphere-egu21-368, 2021.

Plasma turbulence is typically characterized by a preferred directon, that of teh magnetic field. Most plasmas have a coherent average field component and turbulence develop over it. Tokamaks are teh archetypical case with their strong toroidal field. But also solar arcades, solr wind, magnetospheres and ionospheres have that same property. We consider here turbulence in 3D reconnection outflows. Reconnection often has a gudie field to begin with, but even without it, in the outflow there is a significant field residual from the process of reconnection. This macroscopic field organizes the plasma turbulence to form a very anistotropic state. We recenlty, investigted the properties of turbulence at different locations [1]. We deploy now innovative machine learning tools to investigate the outflows and detect the presence of secondary reconnection sites and regions of energy exchange.

[1] Lapenta, G., et al. "Local regimes of turbulence in 3D magnetic reconnection." The Astrophysical Journal 888.2 (2020): 104.

Work supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 776262 (AIDA, www.aida-space.eu).

How to cite: Lapenta, G.: Hunting for reconnection and energy exchange sites in 3D turbulent outflows, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-662, https://doi.org/10.5194/egusphere-egu21-662, 2021.

Magnetohydrostatic (MHS) extrapolations are developed to model 3D magnetic fields and plasma structures in the solar low atmosphere by using measured vector magnetic fields on the photosphere. However, the photospheric magnetogram may be inconsistent with the MHS assumption. By applying Gauss‘ theorem to an isolated active region, we obtain a set of surface integrals of the magnetogram as criteria for a MHS system. The integrals are a subset of Aly’s criteria for a force-free field (FFF). Based on the new criteria, we preprocess the magnetogram to make it more consistent with the MHS assumption and, at the same time, close to the original data. As a byproduct, we also find the boundary integral that is used to compute the energy of a FFF usually underestimates the magnetic energy of an active region.

How to cite: Zhu, X., Wiegelmann, T., and Inhester, B.: Preprocessing of magnetograms for magnetohydrostatic extrapolations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1973, https://doi.org/10.5194/egusphere-egu21-1973, 2021.

Vortices and vortex tubes are ubiquitous in the solar atmosphere and space plasma. In order to identify vortices and to study their evolution, we seek a suitable mathematical criterium for which a dynamical equation exists. So far, the only option available is given by the vorticity, which however is not the optimal criterion since it can be biased by shear flows. Therefore, we look at another criterion, the swirling strength, for which we found an evolution equation, which we suggest as a novel tool for the analysis of vortex dynamics in (magneto-)hydrodynamics. We highlight a few results obtained by applying the swirling strength and its dynamical equation to simulations of the solar atmosphere.

How to cite: Canivete Cuissa, J. R. and Steiner, O.: Vortices evolution in ideal (M)HD, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4713, https://doi.org/10.5194/egusphere-egu21-4713, 2021.

The electrons in the solar wind exhibit an interesting kinetic substructure with many important implications for the overall energetics of the plasma in the heliosphere. We are especially interested in the formation and evolution of the electron strahl, a field-aligned beam of superthermal electrons, in the heliosphere. We develop a kinetic transport equation for typical heliospheric conditions based on a Parker-spiral geometry of the magnetic field. We present the results of our theoretical model for the radial evolution of the electron velocity distribution function (VDF) in the solar wind. We study the effects of the adiabatic focusing of energetic electrons, wave-particle interactions, and Coulomb collisions through a generalized kinetic equation for the electron VDF. We compare and contrast our results with the observed effects in the electron VDFs from space missions that explore the radial evolution of electrons in the inner heliosphere such as Helios, Parker Solar Probe, and Solar Orbiter.

How to cite: Jeong, S.-Y., Verscharen, D., Christian, V., Owen, C., Wicks, R., and Fazakerley, A.: The formation and evolution of the electron strahl in the inner heliosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5152, https://doi.org/10.5194/egusphere-egu21-5152, 2021.

Wave-particle interactions are believed to be one of the most important kinetic processes regulating the heating and acceleration of Solar Wind plasma. One possible explanation to the observed preferential heating of alpha (He⁺²) ions relies on a process similar to a second order Fermi acceleration mechanism. In this model, heavy ions are able to resonate with multiple counter-propagating ion-cyclotron waves, while protons can encounter only single resonances, resulting in the subsequent preferential energization of minor ions. In this work, we address and test this idea by calculating the number of plasma particles that are resonating with ion-cyclotron waves propagating parallel and anti-parallel to an ambient magnetic field in a proton/alpha plasma with cold electrons. Resonances are calculated through the proper kinetic multi-species dispersion relation of Alfven waves. We show that 100% of the alpha population can resonate with counter-propagating waves below a threshold ΔU_αp/v_A<U₀+a(β+β₀)^b in the differential streaming between protons and alpha particles, where U₀=-0.532, a=1.211, β₀=0.0275, and b=0.348 for isotropic ions. This threshold seems to match with constraints of the observed ΔU_αp in the Solar Wind for low values of the proton plasma beta. Finally, it is also shown that this process is limited by the growth of plasma kinetic instabilities, a constraint that could explain alpha-to-proton temperature ratio observations in the Solar Wind at 1 AU.

How to cite: Navarro, R. E., Muñoz, V., Valdivia, J. A., and Moya, P. S.: Feasibility of Ion-cyclotron Resonant Heating in the Solar Wind, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6858, https://doi.org/10.5194/egusphere-egu21-6858, 2021.

All planets of the solar system with an active internal dynamo have a their magnetic dipole oriented perpendicularly or nearly perpendicularly to the solar wind during all or part of their orbit  around the Sun. If, in addition, the planetary rotation is slow, or if the angle between dipole and rotation axis is large, planetary field lines crossing the antisolar axis can become stretched to large distances downstream of the planet. Examples where this may occur are Mercury and Uranus at solstice time, respectively. 

Inspired by these examples, we present a tentative one-dimensional magnetohydrodynamic model of the plasma flowing along the antisolar direction. 

Assuming that the radius of curvature R(z) of the planetary field lines is defined locally as R=D/D', where D(z) is a characteristic  transverse scale of the magnetosphere at a distance z downstream of the planet,  we obtain that the plasma velocity u(z) obeys to a Hugoniot type equation  (M²-1) u'/u =  D'/D,  where M=u/v_A is the Alfvén Mach number. 

The solution for a typical profile D(z) will be discussed. 

How to cite: Pantellini, F.: Fluid model of the plasma flow in the magnetic tail of a planet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7156, https://doi.org/10.5194/egusphere-egu21-7156, 2021.

In collision-poor space plasmas the main physical processes are governed by fluctuations and their interactions with plasma particles. An important source of waves and coherent fluctuations are kinetic instabilities driven by, e.g., protons and electrons exhibiting temperature anisotropies. Unfortunately, such instabilities are generally investigated independently of each other, thereby ignoring their interplay and preventing a realistic treatment of their implications. Here we present the first results of an extended quasilinear approach, which not only confirms linear predictions but also unveils new regimes triggered by cumulative effects of the proton and electron instabilities (e.g., electromagnetic cyclotron, firehose). By comparison to individual excitations combined proton- and electron-induced fluctuations grow and saturate at different intensities as well as different temporal scales in the quasilinear phase. Moreover, the enhanced wave fluctuations can markedly stimulate or inhibit the relaxation of temperature anisotropies, this way highly conditioning the evolution and saturation of instabilities.

How to cite: Hamd, S. M. S., Lazar, M., López, R. R., Wimmer-Schweingruber, R. F., and Fichtner, H.: Cumulative instabilities of anisotropic protons and electrons in the solar wind: New insights from a quasilinear approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7565, https://doi.org/10.5194/egusphere-egu21-7565, 2021.

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

How to cite: Poirier, N., Lavarra, M., Rouillard, A., Indurain, M., Blelly, P.-L., Réville, V., Verdini, A., Velli, M., and Buchlin, E.: Simulating the FIP effect in coronal loops using a multi-species kinetic-fluid model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8369, https://doi.org/10.5194/egusphere-egu21-8369, 2021.

The observation of large scale stable solar magnetic configurations, e.g. sunspots have been done over centuries. But only recently, thanks to modern high-resolution observations solar physicists were able to observe small scale solar features and associated plasma processes, i.e. magnetic bright points, spicules, plasma flows, structure of magnetic fields etc. in great detail. Therefore, advanced theoretical modelling becomes essential to explain observational results, allowing magneto-seismology to be conducted and provide more accurate information about MHD wave propagation and solar atmospheric plasma properties. In this work, we discuss a variety of theoretically constructed 2-3D MHD equilibria obtained by considering different magnetic field configurations and internal flow profiles. The dispersion diagrams and eigenfunctions were obtained numerically for the case where the equilibrium plasma density is modelled as a Gaussian profile with a varying inhomogeneous width and also as a sinc(x) function. The analytic dispersion relation is not required, making this numerical approach a very powerful tool. The proposed numerical approach allows the dispersion diagram and eigenfunctions to be obtained for any inhomogeneous magnetic hydrostatic equilibrium with or without plasma flow. To obtain the numerical solution, the shooting method has been used to match necessary boundary conditions on continuity of displacement and total pressure of the waveguide. The proposed methodology has been successfully tested against well-known analytical results obtained for uniform slab and uniform cylinder geometry. We have found that under coronal conditions, with increasing inhomogeneity in the equilibrium, an additional node appears in the resulting eigenfunctions for the slow body sausage mode, which could be misinterpreted by observers as the existence of an entirely different mode.

How to cite: Skirvin, S., Fedun, V., and Verth, G.: The Dispersion Diagram for Magnetoacoustic Waves in Arbitrarily Structured Solar Waveguides, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8671, https://doi.org/10.5194/egusphere-egu21-8671, 2021.

Turbulence in collisionless magnetized plasmas is a complex multi-scale process involving many decades of scales ranging from large magnetohydrodynamic (MHD) scales down to small ion and electron kinetic scales, associated with different physical regimes. It is well know that the MHD turbulent cascade is driven by the nonlinear interaction of low-frequency Alfvén waves but, on the other hand, the properties of plasma turbulence at sub-ion scales are not yet fully understood. In addition to a great variety of relatively high frequency modes such as kinetic Alfvén waves and whistler waves, magnetic reconnection has been suggested to be a key element in the development of kinetic scale turbulence because it allows for energy to be transferred from large scales directly into sub-ion scales through currents sheets disruption. In this context, an unusual reconnection mechanism driven exclusively by the electrons (with ions being demagnetized), called "electron-only reconnection", has been recently observed for the first time in the Earth’s magnetosheath and its role in plasma turbulence is still a matter of great debate.

Using 2D-3V hybrid Vlasov-Maxwell (HVM) simulations of freely decaying plasma turbulence, we investigate and compare the properties of the turbulence associated with standard ion-coupled reconnection and of the turbulence associated with electron-only reconnection [Califano et al., 2018]. By analyzing the structure functions of the turbulent magnetic field and ion fluid velocity fluctuations, we find that the turbulence associated with electron-only reconnection shows the same statistical features as the turbulence associated with standard ion-coupled reconnection and no peculiar signature related to electron-only reconnection is found in the turbulence statistics. This result suggests that the properties of the turbulent cascade in a magnetized plasma are independent of the specific mechanism associated with magnetic reconnection but depend only on the coupling between the magnetic field and the different particle species present in the system. Finally, the properties of the magnetic field dissipation range are discussed as well and we claim that its formation, and thus the dissipation of magnetic energy, is driven only by the small scale electron dynamics since ions are demagnetized in this range [Arró et al., 2020].

This work has received funding from the European Union Horizon 2020 research and innovation programme under grant agreement No 776262 (AIDA, www.aida-space.eu).

References:

G. Arró, F. Califano, and G. Lapenta. Statistical properties of turbulent fluctuations associated with electron-only magnetic reconnection. , 642:A45, Oct. 2020. doi: 10.1051/0004-6361/202038696.

F. Califano, S. S. Cerri, M. Faganello, D. Laveder, M. Sisti, and M. W. Kunz. Electron-only magnetic reconnection in plasma turbulence. arXiv e-prints, art. arXiv:1810.03957, Oct. 2018.

How to cite: Arrò, G., Califano, F., and Lapenta, G.: Structure functions analysis of sub-ion scale turbulent fluctuations and dissipation range in a magnetized plasma, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9050, https://doi.org/10.5194/egusphere-egu21-9050, 2021.

Coronal Mass Ejections (CMEs) are the main drivers of interplanetary shocks and space weather disturbances. Strong CMEs directed towards Earth can cause severe damage to our planet. Predicting the arrival time and impact of such CMEs can enable to mitigate the damage on various technological systems on Earth. 

We model the inner heliospheric solar wind and the CME propagation and evolution within a new heliospheric model based on the MPI-AMRVAC code. It is crucial for such a numerical tool to be highly optimized and efficient, in order to produce timely forecasts. Our model solves the ideal MHD equations to obtain a steady state solar wind configuration in a reference frame corotating with the Sun. In addition, CMEs can be modelled by injecting a cone CME from the inner boundary (0.1 AU).

Advanced techniques, such as grid stretching and Adaptive Mesh Refinement (AMR) are employed in the simulation. Such methods allow for high(er) spatial resolution in the numerical domain, but only where necessary or wanted. As a result, we can obtain a detailed, highly resolved image at the (propagating) shock areas, without refining the whole domain.

These techniques guarantee more efficient simulations, resulting in optimised computer memory usage and a significant speed-up. The obtained speed-up, compared to the original approach with a high-resolution grid everywhere, varies between a factor of 45 - 100 depending on the domain configuration. Such efficiency gain is momentous for the mitigation of the possible damage and allows for multiple simulations with different input parameters configurations to account for the uncertainties in the measurements to determine them. The goal of the project is to reproduce the observed results, therefore, the observable variables, such as speed, density, etc., are compared to the same type of results produced by the existing (non-stretched, single grid) EUropean Heliospheric FORecasting Information Asset (EUHFORIA) model and observational data for a particular event on 12th of July, 2012. The shock features are analyzed and the results produced with the new heliospheric model are in agreement with the existing model and observations, but with a significantly better performance. 

This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870405 (EUHFORIA 2.0).

How to cite: Baratashvili, T., Verbeke, C., Wijsen, N., Chané, E., and Poedts, S.: Improving CME evolution and arrival predictions with AMR and grid stretching in EUHFORIA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9193, https://doi.org/10.5194/egusphere-egu21-9193, 2021.

Plasma structures with extremely small transverse size (named thin current sheets or TCSs) have been discovered and investigated by spacecraft observations in the Earth's magnetotail, then in other planetary magnetospheres and the solar wind. Their formation is related with complicated dynamic processes in collisionless space plasma near the magnetic reconnection regions. The proposed models describing TCSs in space plasma, based on the assumption of a quasi-adiabatic proton dynamics and magnetized electrons were successful. Various modifications of the initial equilibrium allowed describing such current sheets as the system of current sheets where the central sheet is supported by magnetized electron drifts, and the external sheets are supported by quasi-adiabatic protons and sometimes oxygen ions. Such current configurations are shown to have properties that are completely different from the well-known Harris model, particularly the multiscale structure, embedding and metastability. The structure and evolution of TCSs under the tearing mode as well as the related paradox of complete tearing mode stabilization in configurations with a nonzero normal magnetic field component is highlighted.

This work is supported by the Russian Science Foundation grant № 20-42-04418.

How to cite: Malova, H., Zelenyi, L., Popov, V., and Grigorenko, E.: Thin current sheets as key structures in space plasma, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9219, https://doi.org/10.5194/egusphere-egu21-9219, 2021.

Reference:

• S. Zenitani & T. N. Kato, Multiple Boris integrators for particle-in-cell simulation, Comput. Phys. Commun. 247, 106954, doi:10.1016/j.cpc.2019.106954 (2020)

How to cite: Zenitani, S. and Kato, T.: Multiple Boris solvers for particle-in-cell (PIC) simulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9368, https://doi.org/10.5194/egusphere-egu21-9368, 2021.

Chromospheric evaporations are frequently observed at the footpoints of flare loops in flare events. The evaporations flows driven by thermal conduction or fast electron deposition often have high speed of hundreds km/s. Since the speed of the observed evaporation flows is comparable to the local Alfven speed, it is reasonable to consider the triggering of Kelvin-Helmholtz instabilities. Here we revisit a scenario which stresses the importance of the Kelvin-Helmholtz instability (KHI) proposed by Fang et al. (2016). This scenario suggests that evaporations flows from two footpoints of a flare loop can meet each other at the looptop and produce turbulence there via KHI. The produced KHI turbulence can play important roles in particle accelerations and generation of strong looptop hard X-ray sources. We investigate whether evaporation flows can produce turbulence inside the flare loop with the help of numerical simulation. KHI turbulence is successfully produced in our simulation. The synthesized soft X-ray curve demonstrating a clear quasi-periodic pulsation (QPP) with period of 26 s. The QPP is caused by a locally trapped, fast standing wave that resonates in between KHI vortices.

How to cite: Ruan, W., Xia, C., and Keppens, R.: Turbulence driven by chromospheric evaporations in solar flares, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11065, https://doi.org/10.5194/egusphere-egu21-11065, 2021.

How to cite: Gauthier, G., Chust, T., Le Contel, O., and Savoini, P.: Electromagnetic electron hole generation: theory and PIC simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11078, https://doi.org/10.5194/egusphere-egu21-11078, 2021.

The energy distribution at wave number space is known to be anisotropic in space plasmas. At kinetic scales, the standard Kinetic Alfven Wave model predicts anisotropy scaling of k_par ∝ k_perp^(1/3), whereas the latest models considering the intermittency, or tearing instabilities, predict scalings such as k_par ∝ k_perp^(2/3) and k_par ∝ k_perp^(3/3). Recent numerical simulations also payed considerable attention to this issue. Based on a unified analysis of five-point structure functions of the turbulence in three kinetic simulations, Cerri et al. 2019 obtained a converging result of l_par ∝ l_perp^(3/3). To enrich our knowledge of the anisotropic scaling relation from an observational point of view, we conducted a statistical survey for the turbulence measured by MMS in the magnetosheath. For the 349 intervals with burst mode data, abundant evidence of 3D anisotropy at the sub-proton scale (1-100 km) is revealed by five-point second order structure functions. In particular, the eddies are mostly elongated along background magnetic field B₀ and shortened in the two perpendicular directions. The ratio between eddies’ parallel and perpendicular lengths features a trend of rise then fall toward small scales, whereas the anisotropy in the perpendicular plane appears scale invariant. Moreover, over 30% of the events exhibit scaling relations close to l_par ∝ l_perp^(2/3). In order to explain such signature, additional factors such as intermittency caused by different coherent structures may be required in addition to the critical balance premise.

How to cite: Wang, T., He, J., Alexandrova, O., Dunlop, M., and Perrone, D.: In situ observation of three-dimensional anisotropies and scalings of space plasma turbulence at kinetic scales, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11588, https://doi.org/10.5194/egusphere-egu21-11588, 2021.

The time-dependent magnetofrictional model (TMFM) is a prevalent approach that has proven to be a very useful tool in the study of the formation of unstable structures in the solar corona. In particular, it is capable of incorporating observational data as initial and boundary conditions and requires shorter computational time compared to MHD simulations. To leverage the efficiency of data-driven TMFM and also to simulate eruptive events in the MHD framework, one can apply TMFM up to a certain time before the expected eruption(s) and then go on with simulation in the full or ideal MHD regime in order to more accurately capture the eruption process. However, due to the different evolution processes in these two models, using TMFM snapshots in an MHD simulation is non-trivial with several issues that need to be addressed, both physically and numerically.

In this study, we showcase our progress in using magnetofrictional model results as input to dynamical MHD simulations. In particular, we discuss the incompatibility of the TMFM output to serve as the initial condition in MHD, and show our methods of mitigating this.

As our benchmark test-case, we study the evolution of NOAA active region 12673, which was previously studied using data-driven TMFM by Price et al. (2019).

How to cite: Daei, F., Pomoell, J., Kilpua, E., Price, D., Kumari, A., and Good, S.: Modeling the formation and eruption of coronal structures by linking data-driven magnetofrictional and MHD simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13774, https://doi.org/10.5194/egusphere-egu21-13774, 2021.

Magnetic reconnection is a fundamental physical process that is responsible for releasing the magnetic energy during substorms of planetary magnetotails. Previous studies of magnetic reconnection usually take the two-dimensional (2D) approach, which assumes that reconnection is uniform in the 3rd direction out of the 2D reconnection plane. However, observations suggest that reconnection can be limited in the 3rd direction, such as reconnection at Mercury's magnetotail. It turns out that reconnection can be suppressed when reconnection region is very limited in the 3rd direction. An internal x-line asymmetry along the current direction develops because of the transport of reconnected magnetic flux by electrons beneath the ion kinetic scale, resulting in a suppression region identified in Liu et al., 2019. Under the guidance of a series of 3D kinetic simulations, in this work, we incorporate the length-scale of this suppression region ~10d_i to quantitatively model the reduction of the reconnection rate and the maximum outflow speed observed in the short x-line limit. The average reconnection rate drops because of the limited active region (where the current sheet thins down to the electron inertial scale) within an x-line. The outflow speed reduction correlates with the decrease of the J×B force, that can be modeled by the phase shift between the J and B profiles, also as a consequence of the flux transport. Notably, these two quantities are most essential in defining the well-being of magnetic reconnection, which can tell us when reconnection shall be suppressed.

How to cite: Huang, K., Liu, Y.-H., Lu, Q., and Hesse, M.: Scaling of magnetic reconnection with a limited x-line extent, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13908, https://doi.org/10.5194/egusphere-egu21-13908, 2021.

With a 1-D PIC simulation model, we have investigated the gap formation around 0.5Ω_e of the quasi-parallel whistler-mode waves excited by an electron temperature anisotropy. When the frequencies of excited waves in the linear stage cross 0.5Ω_e, or when they are slightly larger than 0.5Ω_e but then drift to lower values, the Landau resonance can make the electron distribution form a beam-like/plateau population. Such an electron distribution only slightly changes the dispersion relation of whistler-mode waves, but can cause severe damping around 0.5Ω_e via cyclotron resonance. At last, the wave spectrum is separated into two bands with a power gap around 0.5Ω_e. The condition under different electron temperature anisotropy and plasma beta is also surveyed for such kind of power gap. Besides, when only the waves with frequencies lower than 0.5Ω_e are excited in the linear stage, a power gap can also be formed due to the wave-wave interactions, i.e., lower band cascade. Our study provides a clue to reveal the well-known 0.5Ω_e power gap of whistler-mode waves ubiquitously observed in the inner magnetosphere.

How to cite: Chen, H., Gao, X., Lu, Q., and Sauer, K.: Gap formation around 0.5Ωe of whistler-mode waves excited by electron temperature anisotropy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16137, https://doi.org/10.5194/egusphere-egu21-16137, 2021.