Turbulence-driven magnetic reconnection and the magnetic correlation length: Observations from Magnetospheric Multiscale in Earth's magnetosheath

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Standard magnetic reconnection couples with both electron‐ and ion dynamics. Recently, a new type of magnetic reconnection, electron‐only reconnection without the coupling of ion dynamics, has been observed in space. Using a two‐dimensional particle‐in‐cell simulation, we show that in the externally‐driven magnetotail, electron‐only reconnection is a transition from quiet current sheet to standard reconnection. We find that (a) energy conversion j ⋅ E′ is around zero in quiet current sheet but nonzero in electron‐only reconnection, and (b) ion temperature does not change across electron‐only reconnection but peaks at the center of standard reconnection. These two differences can be used as criteria to distinguish magnetotail electron‐only reconnection from quiet current sheet and standard reconnection, respectively. Based on the two criteria, we justify that the MMS 17 June 2017 event is a magnetotail electron‐only reconnection event.

“…Standard reconnection has also been observed to occur in Earth's turbulent magnetosheath (e.g., Retinò et al., 2007; Stawarz et al., 2022). However, Phan et al.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Electron‐Only Reconnection as a Transition From Quiet Current Sheet to Standard Reconnection in Earth's Magnetotail: Particle‐In‐Cell Simulation and Application to MMS Data

Wang

et al. 2022

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“…The estimated shock normal angle is therefore θ bn ≈ 36°, corresponding to a Q ‖ shock. In the MSH, B (Figure 1a) has an average magnitude 〈B〉 = 21 nT and fluctuations of 𝐴𝐴 𝐴𝐴𝐴𝐴∕⟨𝐴𝐴⟩ = √ ⟨|(𝑩𝑩(𝑡𝑡) − ⟨𝑩𝑩⟩)| 2 ⟩∕⟨𝐴𝐴⟩ = 0.92 , which falls in the range of statistically observed fluctuation levels in the MSH (Stawarz et al, 2022).…”

Section: Whistler Observationsmentioning

confidence: 81%

Kinetic Generation of Whistler Waves in the Turbulent Magnetosheath

Svenningsson

Yordanova

Cozzani

et al. 2022

The Earth's magnetosheath (MSH) is the space plasma region downstream of the bow shock where solar wind plasma is heated, slowed down, and deflected around the magnetosphere. Numerous physical processes take place in the MSH, among which are pitch-angle scattering from wave-particle interactions (He et al., 2019), and particle trapping (Ahmadi et al., 2018;Yao et al., 2018), which shape the velocity distributions of the electrons and ions and contribute to the heating of the plasma. Understanding these processes and the conditions in which they arise is an active research topic.The conditions in the MSH depend on the geometry of the bow shock, where it is common to differentiate between two different cases: quasi-parallel (Q ‖ ) and quasi-perpendicular (Q ⊥ ). In the Q ⊥ case, the shock normal angle θ bn (the angle between the bow shock normal direction and the interplanetary magnetic field (IMF)) is larger than 45° (Balogh et al., 2005). Typical for this region is ion pressure anisotropy which favors the mirror mode instability (Dimmock et al., 2015), and particle energization is mainly caused by compression. In the Q ‖ case, θ bn < 45°. Since the MSH is magnetically connected to the IMF, it strongly interacts with the upstream transients and discontinuities hitting the bow shock. The Q ‖ MSH is characterized by significant variations in the magnetic field, particle velocity, density, and temperature. The fluctuations of the plasma parameters have larger amplitude than in the Q ⊥ case. Current sheets (Vörös et al., 2016;Yordanova et al., 2020), high speed jets (Hietala Abstract The Earth's magnetosheath (MSH) is governed by numerous physical processes which shape the particle velocity distributions and contribute to the heating of the plasma. Among them are whistler waves which can interact with electrons. We investigate whistler waves detected in the quasi-parallel MSH by NASA's Magnetospheric Multiscale mission. We find that the whistler waves occur even in regions that are predicted stable to wave growth by electron temperature anisotropy. Whistlers are observed in ion-scale magnetic minima and are associated with electrons having butterfly-shaped pitch-angle distributions. We investigate in detail one example and, with the support of modeling by the linear numerical dispersion solver Waves in Homogeneous, Anisotropic, Multicomponent Plasmas, we demonstrate that the butterfly distribution is unstable to the observed whistler waves. We conclude that the observed waves are generated locally. The result emphasizes the importance of considering complete 3D particle distribution functions, and not only the temperature anisotropy, when studying plasma wave instabilities. Plain Language SummaryThe magnetosheath (MSH) is the region downstream of the Earth's bow shock where solar wind plasma is slowed down, heated, and deflected around the magnetosphere. The angle between the interplanetary magnetic field and the bow shock normal direction determines the properties of the MSH leading to the formation of two distinct c...

“…A recent development in the study of reconnection has been the observation of purely electron‐scale reconnection regions, in which ions do not participate in the reconnection process (Gingell et al., 2019, 2020, 2021; Phan et al., 2018; Stawarz et al., 2022; Wang et al., 2019). This differs from the standard picture of collisionless reconnection (Ishizawa et al., 2004; Malyshkin, 2008; Yamada, 2011), where the reconnection region consists of an electron‐scale layer within a wider ion‐scale diffusion region.…”

Section: Introductionmentioning

confidence: 99%

“…In this work we focus on reconnection in the turbulent environment downstream and in the transition region of quasi‐parallel shocks. Numerous electron‐scale current sheets are observed in these regions, leading to a favorable environment for electron‐scale reconnection (Gingell et al., 2017, 2019, 2020, 2021; Phan et al., 2018; Sharma Pyakurel et al., 2019; Stawarz et al., 2022; Wang et al., 2019). While existing kinetic simulation studies in the shock environment have shown reconnection at both electron and ion scales, the simulations have been two‐dimensional (Bessho et al., 2019; Bessho et al., 2020, 2022; Q. Lu et al., 2021), restricting reconnection to a single plane.…”

Section: Introductionmentioning

confidence: 99%

Electron‐Scale Reconnection in Three‐Dimensional Shock Turbulence

Chen

Bessho

et al. 2022

Magnetic reconnection is a process in which magnetic field lines in a plasma change their topology, often accompanied by the conversion of stored magnetic energy to kinetic energy of accelerated particles (Priest & Forbes, 2000;Yamada, 2011). Reconnection plays an important role in laboratory and space plasma processes, including sawtooth crashes in tokamaks (von Goeler et al., 1974), magnetic substorms in the Earth's magnetosphere (Angelopoulos et al., 2008) and solar flares (Sweet, 1969).A recent development in the study of reconnection has been the observation of purely electron-scale reconnection regions, in which ions do not participate in the reconnection process (