Kelvin–Helmholtz vortices at the magnetopause during northward IMF: multi-satellite observations of energy transport and plasma redistribution

Abstract

The Kelvin–Helmholtz (KH) instability is a fundamental plasma process in many astrophysical environments; its vortices facilitate solar wind energy transport and plasma mixing. We investigate the energy flux density distribution and fluctuations of a typical KH vortex event observed by THEMIS across different magnetopause regions. Power spectral density (PSD) analysis of different energy flux densities reveal that their peaks correspond to the main period with a maximum of approximately 138 s for efficient energy transport. Satellite observations show that the spatial distributions of mass and energy vary markedly across different regions of magnetopause KH vortices. The region near the inner magnetopause is predominantly governed by electromagnetic energy flux density, whereas the area near the outer magnetopause is more significantly influenced by a combination of thermal and kinetic energy flux densities. Mass transport mainly occurred near the outer magnetopause, while plasma heating may have taken place in the outer magnetosphere. Furthermore, we estimate a local, per-unit-area energy transmission fraction across the magnetopause during the KH interval by time integrating the boundary-normal energy flux density. Using upstream OMNI data as a proxy for the incident solar wind energy flux, we infer that up to $$\sim$$ 2.19% of this locally incident energy flux is transmitted to the outer magnetosphere in this event. This study provides observational constraints on how KH vortices in a collisionless boundary layers redistribute energy and plasma across a shear interface, offering a terrestrial benchmark for models of transport and mixing in planetary magnetospheres and other astrophysical shear flows.