Ring current formation and decay: A review of modeling work

Abstract

The ring current is a complex system whose dynamics involve particle transport, particle loss, large-scale electric- and magnetic-field variations, and wave generation. This is a review of major advances in ring current modeling, with emphasis on the understanding of processes that lead to ring current formation and decay. Numerical modeling has led to qualitative and quantitative progress in the understanding of such processes. Significant advances have been made in the understanding of charged-particle transport via unsteady convective access and radial diffusion into the ring current region under both quiescent and stormtime conditions. Stormtime decreases in D st (toward more negative values) can be understood quantitatively as the consequence of enhanced access of plasma sheet particles to the ring current region, especially in association with an enhanced stormtime plasma sheet population. Recovery phase (during which D st decays back upward toward zero) is dominated by loss processes such as charge exchange, Coulomb drag, and wave-particle interactions, as radial transport rate declines to pre-storm levels.