Direct Observation of Magnetic Reconnection Resulting From Interaction Between Magnetic Flux Rope and Magnetic Hole in the Earth's Magnetosheath.

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. Plain Language Summary: Magnetic flux rope (MFR) is a kind of helical magnetic field structure that is frequently observed in the Earth's magnetosphere. At the dayside magnetopause, MFRs are generally generated by the reconnection of the Earth's intrinsic magnetic field and the interplanetary magnetic field, especially when the interplanetary magnetic field points southward. These MFRs tend to grow larger after they are expelled from the reconnection sites and then travel along the magnetopause, and ultimately disintegrate into the cusp. In this study, we provide another potential fate of these magnetopause MFRs. They can interact with the magnetosheath magnetic holes and dissipate through reconnection with multiple magnetic holes. Based on the Magnetospheric Multiscale observation, we provide direct evidence of reconnection between the MFR and the magnetic hole, which has a pivotal role in this scenario. Our results give new insights into the evolution of MFRs at the magnetopause and further the coupling between the solar wind and the Earth's magnetosphere. Key Points: First observation of magnetic reconnection between magnetic flux rope (MFR) and magnetic hole (MH) in the magnetosheathA thin current sheet with typical reconnection signatures was formed at the interface of MFR and MH due to their interactionAn elongated electron diffusion region was detected in the reconnection exhaust [ABSTRACT FROM AUTHOR]