[P-EM16] Magnetospheric Multi Scale (MMS) mission: Accomplishments and Future Plans

[PEM16-P01] Magnetic island formation in reconnecting electron-scale current sheet: MMS observations in the magnetotail

*長谷川 洋¹、Richard Denton²、中村 るみ³、Kevin Genestreti⁴、中村 琢磨³、Kyoung-Joo Hwang⁵、Narges Ahmadi⁶、Tai Phan⁷、Roy Torbert⁴、Jim Burch⁵、Barbara Giles⁸、Dan Gershman⁸、Chris Russell⁹、Robert Strangeway⁹、Per-Arne Lindqvist¹⁰、Yuri Khotyaintsev¹¹、Robert Ergun⁶、斎藤 義文¹ (1.宇宙航空研究開発機構宇宙科学研究所、2.ダートマス大学、3.オーストリア科学アカデミー、4.ニューハンプシャー大学、5.サウスウェスト研究所、6.コロラド大学、7.カリフォルニア大学バークレー校宇宙科学研究所、8.NASAゴダード宇宙飛行センター、9.カリフォルニア大学ロサンゼルス校、10.スウェーデン王立工科大学、11.ウプサラ大学スウェーデン宇宙物理学研究所)

キーワード：磁気リコネクション、電子電磁流体力学、磁気圏尾部、磁気島、地球磁気圏

Magnetic reconnection controls the transport of solar wind mass and energy into Earth's magnetosphere and is the key to explosive energy release in the magnetotail during magnetospheric substorms. A simplest form of magnetic reconnection in space occurs in the magnetotail where the magnetic fields are nearly antiparallel, no significant jumps in plasma parameters exist across the current sheet, and no significant turbulence is seen in the inflow (lobe) regions. The Magnetospheric Multiscale (MMS) spacecraft, however, have revealed complex features such as a displacement of the stagnation point relative to the X point in the outflow jet direction even for magnetotail reconnection. Here, using in situ observations from MMS in the magnetotail, we present evidence of secondary magnetic island formation in a reconnecting electron-scale current sheet in the magnetotail detected by MMS. The electron diffusion region (EDR) of the event, first reported by Zhou et al. (ApJ, 2019), was recovered by two reconstruction techniques. One is based on electron magnetohydrodynamics equations (Sonnerup et al., JGR, 2016), and the other on polynomial expansion of the magnetic field using instantaneous measurements by the four spacecraft of the magnetic field and particle current density (Denton et al., JGR, 2020). The results from both reconstructions show that a small-scale magnetic island was growing in a reconnecting current sheet with a thickness of about one electron inertial length, consistent with fully kinetic simulations of antiparallel reconnection (Daughton et al., PoP, 2006). It suggests that secondary island formation is an intrinsic process in the EDR of antiparallel reconnection, and reconnection may drive turbulence energy cascade at sub-ion scales by creating sub-ion-scale islands in electron-scale current sheets.

References:
Daughton, W., J. Scudder, and H. Karimabadi, Fully kinetic simulations of undriven magnetic reconnection with open boundary conditions, Phys. Plasmas, 13, 072101, https://doi.org/10.1063/1.2218817, 2006.
Denton, R. E., R. B. Torbert, H. Hasegawa, et al., Polynomial reconstruction of the reconnection magnetic field observed by multiple spacecraft, Journal of Geophysical Research: Space Physics, 125, https://doi.org/10.1029/2019JA027481, 2020.
Sonnerup, B. U. O., H. Hasegawa, R. E. Denton, and T. K. M. Nakamura, Reconstruction of the electron diffusion region, J. Geophys. Res. Space Physics, 121, 4279-4290, doi:10.1002/2016JA022430, 2016.
Zhou, M., X. H. Deng, Z. H. Zhong, et al., Observations of an electron diffusion region in symmetric reconnection with weak guide field, Astrophys. J., 870, 34, https://doi.org/10.3847/1538-4357/aaf16f, 2019.