On the Dipolarization Front and Magnetopause: 2. Evidence of Interchange Instability at Magnetopause

Abstract

Interchange instability is a macroscopic instability that commonly develops when the centrifugal acceleration opposes the acceleration induced by the density gradient at the interface between two regions. Over the past two decades, extensive studies have focused on this instability, particularly at dipolarization fronts. However, due to the similar physical properties of these two boundary layers, it has also been implicated that this instability may develop at the magnetopause (W. D. Fu, Fu, Cao, et al., 2025, https://doi.org/10.1029/2025ja033633). In this work, we analyze data from the Magnetospheric Multiscale (MMS) mission to identify a series of quasi-periodic magnetic field disturbances during a subsolar magnetopause crossing event. Alongside these magnetic field disturbances, the magnetospheric plasma population alternated with the magnetosheath population. By examining solar wind conditions and performing the timing analysis, we confirmed that these observations were not due to temporal variations from inward or outward motions of the magnetopause, but rather corresponded to spatial magnetic field structures. We further demonstrate that these structures do not meet the criterion for mirror mode, but instead fulfill the unstable condition for the interchange mode, revealing that such structures were formed by the interchange instability. This discovery offers new insights into the plasma exchange between the magnetosphere and solar wind, and opens promising avenues for further exploration with the upcoming Solar-Wind-Magnetosphere-Ionosphere Link Explorer (SMILE) mission through its global-scale imaging.