[P-EM15] Dynamics of Magnetosphere and Ionosphere

[PEM15-04] Magnetopause reconnection under sub-Alfvenic solar wind with northward magnetic field

*長谷川 洋¹、Denton Richard²、Chen Li-Jen³、Hu Qiang⁴、西野 真木¹、Hwang Kyoung-Joo⁵ (1.JAXA宇宙科学研究所、2.ダートマス大学、3.NASAゴダード宇宙飛行センター、4.アラバマ大学、5.サウスウェスト研究所)

キーワード：磁気リコネクション、太陽風、磁気圏界面、地球磁気圏

Solar wind is a supersonic plasma flow emanating from the Sun, but on rare occasions the solar wind at 1 AU can be slower than the local Alfvén speed. Such a sub-Alfvénic solar wind was observed on 24 April 2023 when a magnetic cloud, a substructure of coronal mass ejections, impinged on Earth’s magnetosphere. We present observations on this day by the Magnetospheric Multiscale (MMS) spacecraft around the dayside magnetopause during an interval of sub-Alfvénic solar wind with northward interplanetary magnetic field, the conditions for which the solar wind-magnetosphere interaction is poorly understood. Our analysis of MMS data shows that magnetic reconnection at the observed magnetopause was more efficient than under typical high Alfvén Mach number solar wind conditions. This more efficient reconnection can cause complex interaction of reconnected magnetic field lines, possibly leading to more vigorous transport of solar wind plasmas into the magnetosphere, and can energize ions and electrons more efficiently. The results could provide significant insights into coupling between the solar wind and other planets, such as at Mercury, or between planetary magnetospheric plasmas and moons under low Alfvén Mach number conditions.