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 (R_i), may appear anomalously high, whereas that normalized by electron parameters (R_e) 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 (ρ_i) 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.