Xuanye Ma | Searcharxiv

arXiv2026

Simultaneous Mars-orbit observations reveal Kelvin-Helmholtz instability-driven bulk atmospheric ion escape

Atmospheric ion escape driven by the solar wind is a key process controlling the long-term loss of the Martian atmosphere. Localized plasma clouds can carry substantial fluxes of planetary ions away from Mars, representing episodes of bulk escape. However, their origin has remained unclear due to the absence of simultaneous upstream measurements. Using joint observations from the MAVEN and Tianwen-1 missions, which provide real-time upstream monitoring, we present direct evidence that these plasma clouds are nonlinear wave packets generated by the Kelvin-Helmholtz instability (KHI). The spatial scale of KH waves is constrained for the first time via two-point measurements. Ion fluxes within plasma clouds are one to two orders of magnitude higher than those in typical steady-state escape channels. Our results indicate that KHI is an important process for solar wind coupling to planetary upper atmospheres and plays a crucial role in shaping atmospheric ion escape for unmagnetized planets.

physics.space-ph↗

arXiv2018

Magnetospheric Multi-Scale Observations of High-Energy Electrons and Protons in the Vicinity of Southern High-Altitude Cusp Boundaries

Recent Magnetosphere Multiscale (MMS) observations found 238 high energy (> 40 keV) electron "leaking" events in the the magnetosheath [Cohen et al., 2017]. While several sources have been proposed, the dominant mechanism or origin of these particles is not well understood. We have analyzed MMS locations during these these events and found that most of these electron leaking events were observed close to the southern high-altitude cusp and associated boundaries, so these events may have a high-latitude source. Here we present a new case study of observations of a MMS encounter of southern magnetospheric cusp boundaries. In the magnetosheath side of the southern cusp, MMS observes both parallel streaming energetic ions, as well as a population with 90 degree pitch angles. Subsequently, MMS detects plasma flows and magnetic field rotation consistent with magnetic reconnection (operating above and dawn-ward of the MMS spacecraft), finally entering a depressed magnetic field region with nearly stagnant flow. The depressed field region is occupied by high-fluxes of trapped high-energy electrons and protons, which resemble the Cluster observations of cusp diamagnetic cavities at the northern hemisphere [Nykyri et al., 2011a]. However, the local magnetic field geometry during the prevailing IMF orientation is not favorable for magnetic reconnection to directly create a cavity in this location. We show that the plasma flows that were observed prior to cavity observation satisfy the onset condition for the Kelvin-Helmholtz instability for 50 percent of all available k-vector directions.

physics.space-ph↗