Ion energization and transport associated with magnetic dipolarizations

Abstract

Ion energization in the magnetotail during substorms is examined by simulating a modest substorm event that occurred on 7 February 2009. The simulation scheme combines global magnetohydrodynamic (MHD) modeling of the magnetosphere driven by realistic upstream solar wind conditions, with a large-scale kinetics (LSK) simulation. Multiple earthward propagating dipolarizations driven by reconnection outflow jets are modeled by the MHD simulation. Ion trajectories in the LSK simulation show that ions that originated near the reconnection site first gained energy nonadiabatically and then gained energy adiabatically as they "caught up with and then rode on" the earthward propagating dipolarizations. Consequently, the high-energy (>25 keV) ion fluxes were enhanced where and when the dipolarizations intensified. High-speed flows in narrow channels controlled the ion earthward transport in the outer magnetosphere due to the dominant E × B drift. The mechanisms of nonlocal energization by dipolarizations and transport controlled by high-speed flows operate similarly for electrons as described by Ashour-Abdalla et al. (2011) and Pan et al. (2014).