Spatial Dependence of Ion-Kinetic Instabilities in the Earth's Magnetosheath: MMS Observations

Abstract

The Earth's magnetosheath plasma frequently exhibits unequal temperatures parallel and perpendicular to the background magnetic field. This temperature anisotropy is crucial in exciting and dissipating electromagnetic fluctuations in various plasma environments. Leveraging a comprehensive dataset comprising sub-ion scale measurements from NASA's Magnetospheric Multiscale Mission, our study unveils insights into the spatial evolution and parametric dependence of different ion kinetic instabilities within the Earth's magnetosheath. We observe a remarkable spatial dependence on the occurrence of kinetic instabilities. The condition for the mirror-mode instability exhibits a significantly higher prevalence near the subsolar magnetopause compared to the flank regions. The condition for the oblique firehose instability is more prominent near the bow shock region than in the vicinity of the magnetopause. Furthermore, the occurrence of these instabilities and their spatial distribution are linked to the plasma's upstream conditions. Our study offers new insights into the nature of ion kinetic instabilities in the Earth's magnetosheath and similar plasma environments.