Orals: Mon, 28 Apr | Room 1.14
Magnetic reconnection is a fundamental plasma process responsible for the sometimes explosive release of magnetic energy in space and laboratory plasmas. Inside the diffusion regions of magnetic reconnection, the plasma becomes demagnetized and decouples from the magnetic field, enabling the change in magnetic topology necessary to power the energy release over larger scales. Since it was launched in 2015, the Magnetospheric MultiScale (MMS) mission has significantly advanced the understanding of the particle dynamics key to magnetic reconnection by providing high-resolution, in-situ measurements able to resolve ion and electron kinetic scales that have confirmed theoretical predictions, revealed new phenomena, and refined existing models. These breakthroughs are critical for understanding not only space plasmas but also laboratory and astrophysical plasmas where magnetic reconnection occurs. In this talk, we give a brief review and present some recent results of selected topics related to the ion and electron dynamics occurring within the diffusion regions.
How to cite: Norgren, C. and the ISSI MMS Workshop Team: Plasma dynamics in the diffusion regions of magnetic reconnection, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2163, https://doi.org/10.5194/egusphere-egu25-2163, 2025.
Alongside magnetic reconnection, turbulence is another fundamental nonlinear plasma phenomenon that plays a key role in energy transport and conversion in space and astrophysical plasmas. From a numerical, theoretical, and observational perspective there is a long history of exploring the interplay between these two phenomena in space plasma environments; however, recent high-resolution, multi-spacecraft observations have ushered in a new era of understanding this complex topic. The interplay between reconnection and turbulence is both complex and multifaceted, and can be viewed through a number of different interrelated lenses - including turbulence acting to generate current sheets that undergo magnetic reconnection (turbulence-driven reconnection), magnetic reconnection driving turbulent dynamics in an environment (reconnection-driven turbulence) or acting as an intermediate step in the excitation of turbulence, and the random diffusive/dispersive nature of the magnetic field lines embedded in turbulent fluctuations enabling so-called stochastic reconnection. In this talk, we will discuss the current state of knowledge on these different facets of the interplay between turbulence and magnetic reconnection in the context of collisionless plasmas. Particular focus will be given to several key regions in Earth’s magnetosphere – namely, Earth’s magnetosheath, magnetotail, and Kelvin-Helmholtz vortices on the magnetopause flanks – where NASA’s Magnetospheric Multiscale (MMS) mission has been providing new insights into the topic. Results revealed by MMS will be contrasted with other plasma regions such as the solar wind and paths forward in the study of this complex topic, which will potentially be opened by future missions such as ESA’s proposed Plasma Observatory and NASA’s HelioSwarm, will be discussed.
How to cite: Stawarz, J. E., Muñoz, P. A., Bessho, N., Bandyopadhyay, R., Nakamura, T., Eriksson, S., Graham, D., Büchner, J., Chasapis, A., Drake, J. F., Shay, M. A., Ergun, R. E., Hasegawa, H., Khotyaintsev, Y. V., Swisdak, M., and Wilder, V.: The Interplay Between Collisionless Magnetic Reconnection and Turbulence, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14969, https://doi.org/10.5194/egusphere-egu25-14969, 2025.
Magnetic reconnection converts magnetic field energy into particle energy by breaking and reconnecting magnetic field lines. Magnetic reconnection is a kinetic process that generates a wide variety of kinetic waves via wave-particle interactions. Kinetic waves have been proposed to play an important role in magnetic reconnection in collisionless plasmas by, for example, contributing to anomalous resistivity and diffusion, particle heating, and transfer of energy between different particle populations. These waves range from below the ion cyclotron frequency to above the electron plasma frequency and from ion kinetic scales down to electron Debye length scales. In this presentation, we describe the progress made in understanding the relationship between magnetic reconnection and kinetic waves. We focus on the waves in different parts of the reconnection region, namely, the diffusion region, separatrices, outflow regions, and jet fronts. Particular emphasis is placed on the recent observations from the Magnetospheric Multiscale (MMS) spacecraft and numerical simulations, which have substantially increased the understanding of the interplay between kinetic waves and reconnection. Some of the ongoing questions related to waves and reconnection are discussed.
How to cite: Graham, D. and the ISSI magnetic reconnection workshop team: The Role of Kinetic Instabilities and Waves in Collisionless Magnetic Reconnection, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11235, https://doi.org/10.5194/egusphere-egu25-11235, 2025.
Recent spacecraft observations have shown that magnetic reconnection occurs commonly in turbulent environments at shocks. Here, we study magnetic reconnection at a quasi-perpendicular shock by using a two-dimensional particle-in-cell simulation. Magnetic field lines are bent by the back-streaming reflected ions, which form a current sheet in the foot region, and then electron-scale reconnection occurs when the current sheet is fragmented at the shock front. Collective properties of the reconnection sites from the shock transition to the downstream region are analyzed by adopting a statistical approach to the simulation data. Reconnecting current sheets are found to be densely distributed near the shock front, with a reconnection electric field larger than those in the downstream region. By tracing a reconnection site from its formation until it is convected downstream, we show the reconnection proceeds intermittently after an active stage near the shock front. Our tracing further shows that, in addition to being originated from the shock front, reconnection in the downstream region can also occur locally, driven by turbulent flows therein. The results help us better understand the evolution of electron-scale reconnection at a perpendicular shock.
How to cite: Lu, Q. and Guo, A.: Magnetic Reconnection in the downstream of Quasi-perpendicular Shock , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6929, https://doi.org/10.5194/egusphere-egu25-6929, 2025.
The occurrence of magnetic reconnection is usually of pivotal importance regarding the evolution of magnetized astrophysical systems. Among others, diamagnetic suppression is a mechanism that can prevent reconnection from developing. Over the last decade, many studies have suggested from statistical analysis of spacecraft observations, that diamagnetic suppression is the dominant mechanism controlling whether reconnection occurs or not, in many space plasma environments, from planetary magnetospheres to the solar wind and heliopause.
This study shows that previous interpretations of the data were based on a theoretical prediction that is inconsistent with the original numerical models of diamagnetic suppression, and that the statistical separation between current sheets classified as either reconnecting or not thus cannot be explained by this effect.
This proposition is based on the observation that the magnetic shear and difference in plasma beta across current sheets classified as either reconnecting or not are well separated by theoretical predictions.
This study derives the condition for the diamagnetic suppression of magnetic reconnection in asymmetric current sheets and show that is is entirely determined by the magnetic field amplitude asymmetry and shear angle but not on the plasma $\beta$.
Furthermore, we show that an observational bias leads to a similar statistical separation simply because outflow speeds expected from reconnection strongly depend on both the magnetic shear and plasma $\beta$, and low velocity jets become increasingly hard to observe when they become comparable to the surrounding flow fluctuation level, preventing the conclusion that reconnection is suppressed in those conditions.
We furthermore show that well detected jets are found in conditions where, in contrast, reconnection should be suppressed, and conclude that the role of diamagnetic suppression at the Earth's magnetopause remains unclear.
How to cite: Aunai, N., Michotte de Welle, B., Ghisalberti, A., and Lavraud, B.: Is there Evidence For Diamagnetic Drift Suppressing Magnetic Reconnection at the Earth's Magnetopause?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11119, https://doi.org/10.5194/egusphere-egu25-11119, 2025.
We report in situ observation of magnetic reconnection between magnetic flux rope (MFR) and magnetic hole (MH) in the magnetosheath by the Magnetospheric Multiscale mission. The MFR was rooted in the magnetopause and could be generated by magnetopause reconnection therein. A thin current sheet was generated due to the interaction between MFR and MH. The sub-Alfvénic ion bulk flow and the Hall field were detected inside this thin current sheet, indicating an ongoing reconnection. An elongated electron diffusion region characterized by non-frozen-in electrons, magnetic-to-particle energy conversion, and crescent-shaped electron distribution was detected in the reconnection exhaust. The observation provides a mechanism for the dissipation of MFRs and thus opens a new perspective on the evolution of MFRs at the magnetopause. Our work also reveals one potential fate of the MHs in the magnetosheath which could reconnect with the MFRs and further merge into the magnetopause.
How to cite: Wang, S.: Direct observation of magnetic reconnection resulting from interaction between magnetic flux rope and magnetic hole in the Earth’s magnetosheath, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2808, https://doi.org/10.5194/egusphere-egu25-2808, 2025.
The recently discovered electron-only reconnection has drawn great interests due to abnormal features like lack of ion outflows and high reconnection rates. Using particle-in-cell simulations, we investigate their physical mechanisms. The reconnection rate, when normalized by ion parameters (Ri), may appear anomalously high, whereas that normalized by electron parameters (Re) remains ~0.1. We propose that the essence of high is insufficient field line bending outside the electron diffusion region, indicating an incomplete development of the ion diffusion region. It may result from bursty reconnection in thin current sheets, or small system sizes. The ion outflow diminishes at high when the gyroradius (ρi) exceeds the system size. Low-velocity ions still experience notable acceleration from Hall fields. However, a local distribution includes many high-velocity ions that experience random accelerations from different electric fields across , resulting in near-zero bulk velocities. Our study helps understand reconnection structures and the underlying physics for transitions between different regimes.
How to cite: Wang, S., Fan, C.-Y., Zhou, X.-Z., Lu, S., Lu, Q.-M., Pyakure, P., Zong, Q.-G., and Liu, Z.-Y.: New Insights on the High Reconnection Rate and the Diminishment of Ion Outflow, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3165, https://doi.org/10.5194/egusphere-egu25-3165, 2025.
The reconnection electric field is an essential part in magnetic reconnection. In 2D symmetric magnetotail reconnection, the balance of this electric field is analyzed from the generalized Ohm’s law or the electron momentum equation, showing that electron off-diagonal pressure term plays an important role in the electron diffusion region in which electrons break the frozen-in condition. Previous studies have attributed this off-diagonal pressure term to agyrotropic meandering electrons. Here, we examine the gradient of electron pressure (stress) tensor term from the Vlasov equation, enabling a direction evaluation from electron distributions. Our results show that meandering electrons and inflow electrons can both contribute to the electron off-diagonal pressure (stress) term. Before inflow electrons reach to the central current sheet and become pitch angle mixed, they can be gradually demagnetized and decelerated, so the electron pressure (stress) gradient appears between the edge and central electron current sheet.
How to cite: Tang, B., Guo, W., and Li, W.: On the gradient of electron pressure (stress) tensors in magnetotail reconnection, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8003, https://doi.org/10.5194/egusphere-egu25-8003, 2025.
Magnetic reconnection is a fundamental process driving charged particle acceleration in space plasma environments. Traditionally, theoretical and simulation models of this acceleration are validated using in-situ spacecraft measurements from reconnection regions in the near-Earth magnetosphere. In this presentation, we showcase observations revealing that electron acceleration during reconnection can be far more efficient than previously estimated, producing electron populations with energies reaching several MeV. Remarkably, these bursts occur even in regions where the thermal electron energies are below 1 keV. These observations, made possible by recent low-altitude CubeSat missions monitoring magnetotail electron fluxes, provide new insights into the mechanisms driving electron acceleration in Earth's magnetotail.
How to cite: Zhang, X.-J., Artemyev, A., Li, X., Arnold, H., Angelopoulos, V., Turner, D., Shumko, M., Runov, A., Mei, Y., and Xiang, Z.: Observations of Relativistic and Ultra-Relativistic Electron Bursts in Earth's Magnetotail: The Role of Magnetic Reconnection in Electron Acceleration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8021, https://doi.org/10.5194/egusphere-egu25-8021, 2025.
The aim of the study is to investigate tearing-driven magnetic reconnection in the context of weakly collisional astrophysical plasmas. We present here results from two-dimensional hybrid simulations using modified periodic conditions with a topology akin to the Möbius strip. Our primary focus is the global energy conversion during the non-linear stage of the tearing instability. Conversion of electromagnetic to plasma bulk speed energy is evaluated by the j.E term, while conversion from bulk speed to thermal energy is evaluated by the pressure-strain term. Signatures of the firehose instability are also observed within the magnetic islands (or plasmoids), located between the different reconnection sites. The firehose instability, caused by the proton temperature being higher parallel than perpendicular to the local magnetic field, constrains the plasma temperature anisotropy. This then regulates the conversion of bulk speed to thermal energy as indicated by the temporal evolution of the pressure-strain.
How to cite: Berriot, E., Hellinger, P., Alexandrova, O., and Alexandrova, A.: Tearing driven reconnection: interplay between heating and kinetic instabilities (2D hybrid Möbius simulations), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11451, https://doi.org/10.5194/egusphere-egu25-11451, 2025.
Posters on site: Tue, 29 Apr, 10:45–12:30 | Hall X4
Magnetic reconnection is found to be initiated by the electron dynamics recently in the magnetotail. As the electron current layer is generated, it is still unclear when and where the reconnection will be triggered. In this talk, I will show one example of such an evolving process of the electron current layer. It is found that the reconnection is triggered in a localized area away from the current sheet center where the reconnection is supposed to be triggered based on the strong energy dissipation, electron crescent distribution. Furthermore, the lower hybrid waves are detected in the location where the reconnection is triggered and cause the strong energy dissipation. The observations indicate that the reconection is triggered by the lower hybrid waves.
How to cite: Wang, R., Zhan, C., Lu, S., and Lu, Q.: Magnetic reconnection triggered in a localized region across the current sheet in the magnetotail , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2245, https://doi.org/10.5194/egusphere-egu25-2245, 2025.
Magnetic reconnection is an explosive phenomenon occurring in the space environment, where the magnetic topology is altered and the energy is converted to the plasma. It can account for certain physical processes involved with rapid and massive energy transfer, such as the ones in solar flares and substorm. The term, reconnection rate, is adopted to quantitively estimate the progress of the reconnection. A higher reconnection rate corresponds to a faster reconnection as well as the energy conversion burst. The reconnection rate is sensitive to current sheet configurations and plasma properties, such as the current sheet thickness. From the statistical results of the observations, it is suggested that a thicker current sheet corresponds to a slower ion and electron jets. In this study, we attempt to uncover this relevance by performing theoretical analysis and a series of particle-in-cell (PIC) simulations. Particularly, we focus on the peak reconnection rate as it can reflect the maximum energy conversion rate during the reconnection process. Two types of scaling laws of peak reconnection rate with the current sheet thickness are found, when this thickness increases from the electron-scale to the ion-scale. Our results establish a model to predict the reconnection rate and the energy conversion depending on the current sheet thickness.
How to cite: Xiong, Q. and Huang, S.: Dependence of Reconnection Rate and Energy Conversion on the Initial Current Sheet Thickness, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2979, https://doi.org/10.5194/egusphere-egu25-2979, 2025.
Magnetic flux ropes (FRs) are commonly observed in the universal plasmas, in which various dynamic processes can be embedded and thus become important places for energy conversion. Previous observations generally suggested that the energy conversion inside FRs is from the field to particles. Interestingly, taking advantage of the Magnetospheric Multiscale (MMS) mission, we present here a newly observed magnetotail FR with strong particle-to-field energy conversion. Meanwhile, we have revealed that such energy conversion is driven by an intense electron-carried field-aligned current (FAC) and parallel electric field. Continually, based on the analysis of the electron velocity distribution functions (VDFs) and the power spectral density (PSD) of the parallel electric field, we further discuss that the energy conversion probably results in the enhancement of the parallel electric field due to the anti-parallel electron beam. This study essentially improves the understanding of the energy conversion inside the magnetotail flux ropes.
How to cite: Du, C., Fu, H., and Cao, J.: Particle-to-field energy conversion inside a magnetotail flux rope, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7459, https://doi.org/10.5194/egusphere-egu25-7459, 2025.
The tearing mode instability may develop in Harris type current sheets with antiparallel magnetic field. In this study, we study the tearing mode instability in the Harris sheet equilibrium using two-dimensional, linear and nonlinear resistive magnetohydrodynamic (MHD) models with isotropic pressure. We calculate the linear growth rates and eigenmode structures based on the linear MHD model which are used as initial perturbations in the MHD simulations for the full evolution of nonlinear tearing mode instability. Our primary focus is on the effects of various background density profiles on the linear growth rate and nonlinear evolution and saturation of the tearing mode instability. Additionally, we examine the effects of thermodynamic conditions on the tearing mode instability.
How to cite: Chang, C.-K. and Hau, L.-N.: MHD simulations of linear and nonlinear resistive tearing-mode instability in Harris sheet equilibrium, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3941, https://doi.org/10.5194/egusphere-egu25-3941, 2025.
Recently, a new type of magnetic reconnection, electron-only reconnection—where there is no obvious ion flow and heating—has been observed in various plasma environments. Previous kinetic simulations have shown that electron-only reconnection is a precursor of standard reconnection. By performing a two-dimensional (2-D) particle-in-cell (PIC) simulation, we investigate the evolution of electron-only magnetic reconnection to standard magnetic reconnection in a current sheet, whose initial width is of the electron inertial length. In the electron-only reconnection stage, electron outflow produces the electron-scale Bz pileup, and ions are slightly accelerated in the outflow direction by the Hall electric field force. As the reconnection electric field expands and Bz is piled up to the ion scale, ions start to be further accelerated inside the IDR and reflected by the Bz to the outflow direction. With Bz pileup as the bond, ions gradually transit from being accelerated by the Hall electric field to being coupled in reconnection by the Lorentz force.
How to cite: Guan, Y., Lu, Q., Lu, S., and Wang, R.: Evolution of Magnetic Reconnection in Electron-scale Current Sheets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5523, https://doi.org/10.5194/egusphere-egu25-5523, 2025.
Plasma waves are widely observed in the Earth's space, playing a crucial role in the heating and accelerating plasmas, cascading turbulent energy, and facilitating energy conversion during magnetic reconnection. Simulation studies have shown that high-speed electron beams can excite various plasma waves under different plasma environments. High-speed electron flows (HSEFs) are mainly observed near the X-line and drive various types of plasma instabilities and plasma waves, affecting the electron-scale dynamics. We have conducted a systematic statistical study of the super-Alfvénic high-speed electron flows in the Earth magnetotail, using NASA’s Magnetospheric Multiscale (MMS) mission observations from 2017 to 2021, and finally identified 642 events characterized by the electron bulk speed exceeding 5000 km/s. In the vicinity of the HSEFs, various types of electrostatic and electromagnetic waves are observed, their types, characteristics, and relationship with the HSEFs remain unknown. Here, we firstly perform a statistical analysis of the plasma waves in the HSEFs. Only 38.6% and 43.3% of the HSEFs are associated with parallel and perpendicular electric field waves, respectively. For the parallel electric field fluctuations, 60% of them have their frequencies between 0.1 and 1 electron cyclotron frequency (fce), which may be attributed to electrostatic solitary waves driven by electron two-stream instability. For the perpendicular electric field fluctuations, 76.6% of them have their frequencies concentrated around low hybrid frequency, possibly related to the density depletion at the speed peak of HSEFs. For both parallel and perpendicular electric field fluctuations with frequencies larger than fce, they are mainly observed near the neutral sheet, corresponding to langmuir waves and upper hybrid waves, respectively.
How to cite: Liu, H., Li, W., Liu, K., Tang, B., and Wang, C.: Plasma waves in the high-speed electron flows, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8841, https://doi.org/10.5194/egusphere-egu25-8841, 2025.
The magnetic reconnection rate at the magnetopause critically determines how the magnetosphere as a whole couples to the solar wind. Its direct measurement, however, is extremely challenging. Estimates based on single event analysis often yield results with uncertainties of the order of the estimate itself, so are those from statistical analysis, so far limited to a small number of events.
In this study, we propose four independent estimates of the reconnection rate from a large statistical approach based on machine learning detection, on about one million in situ measurements in the vicinity of the subsolar magnetopause. Results clearly show how the component of the magnetic field and bulk velocity normal to the magnetopause increase with the IMF clock angle as expected on-going from reconnection. Their ratio to tangential component is shown to be constant and about 0.1 for all IMF clock angles larger than 60°.
How to cite: Michotte de Welle, B., Aunai, N., Connor, H., Sibeck, D., Lavraud, B., Génot, V., Ghisalberti, A., and Jeandet, A.: Statistical estimate of the magnetopause reconnection rate as a function of the interplanetary magnetic field clock angle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13325, https://doi.org/10.5194/egusphere-egu25-13325, 2025.
Magnetic shear and flow shears form across Earth’s magnetopause when shocked solar winds flow around Earth. Previous studies have shown that these two kinds of shears can similarly affect magnetopause reconnection. However, a direct investigation to evaluate their relative importance is lacking. In this study, we focus on simultaneous magnetopause reconnection observed by Magnetospheric Multiscale mission (MMS) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft at different magnetopause locations to quantitatively evaluate the magnetic shear and flow shear effects. In these observations, the overall effect of magnetic shear (the normalized guide field < 1) is limited unless the guide field is large enough to suppress reconnection, while the flow shear can significantly affect the observed reconnection outflow speed primarily by introducing non-zero X-line motion. Finally, we propose a new relationship combining magnetic and flow shear effects by assuming the X-line drift motion is independently affected by these two effects, which shows that X-line drift speed is dominated by the magnetosheath flow, and the suppression of reconnection is more likely to occur under strong guide field conditions. This study deepens our understanding on magnetopause reconnection occurrence and reconnection behaviors in large scales.
How to cite: Zhang, C., Tang, B., Li, W., Sang, L., Liu, H., and Li, T.: Effects of magnetic shear and flow shear on magnetopause reconnection: Simultaneous observations from MMS and THEMIS, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7782, https://doi.org/10.5194/egusphere-egu25-7782, 2025.
We have developed a new Adaptive Mesh Refinement (AMR) version of the Gauss-Law satisfying Energy Conserving Semi-Implicit Method (GL-ECSIM) and implemented it into the Flexible Exascale Kinetic Simulator (FLEKS). The semi-implicit Particle-In-Cell (PIC) method is particularly well suited for AMR, because, unlike in explicit PIC, the cell size does not have to resolve the Debye length for stability. In contrast with the earlier Multi-Level-Multi-Domain semi-implicit PIC algorithm developed by Innocenti+, the new algorithm uses a single set of particles over the whole domain. Particles are split and merged as needed by efficient and accurate methods. The coarser level receives both the field information and the phase space distribution (through the particles) from the fine level. The fine level uses the coarse level as boundary condition. The new algorithm satisfies Gauss Law on the entire domain, including grid resolution changes. We show various tests confirming the accuracy and robustness of the new algorithm. In particular, we simulate magnetic reconnection with an ion-electron mass ratio of 64. The AMR resolves the electron scales near the reconnection site, while the grid is eight times coarser elsewhere matching the ion scales. The overall speed up is at least tenfold compared to a uniformly fine grid simulation.
How to cite: Arshad, T., Chen, Y., and Toth, G.: Developing Adaptive Mesh Refinement for Semi-Implicit Parcticle-in-Cell Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3796, https://doi.org/10.5194/egusphere-egu25-3796, 2025.
