Energetic particle loss through the magnetopause: A combined global MHD and test-particle study

Abstract

We study the spatiotemporal characteristics of energetic particle losses from the magnetosphere using test-particle trajectories in electromagnetic fields from a global magnetosphere magnetohydrodynamic (MHD) simulation. We use a dynamically evolving distribution of high-resolution electromagnetic fields from the Lyon-Fedder-Mobarry global MHD model and trace large ensembles of 100 keV hydrogen and oxygen ions as well as electrons from a near-Earth plasma sheet location through their escape from the magnetosphere. In agreement with recent MMS observations, we demonstrate that both ions and electrons have access to and escape throughout the dayside magnetopause, including magnetically drift-shadowed regions. Also, in agreement with MMS observations, the depth of penetration and persistence of particles in the magnetosheath has a clear mass dependence, heavier particles penetrating further and lingering longer. We demonstrate both magnetic local time and latitude dependence of particles losses as manifested by their crossings of the open-closed boundary and relate them to the complex field topology. Finally, we establish a significant role of Kelvin-Helmholtz instability in facilitating particle losses at the magnetopause flanks.