The Effect of Different Loss Mechanisms on Ring Current Dynamics Based on The STRIM Model 

Abstract

Charge exchange, Coulomb collisions, and field line curvature scattering (FLCS) are among the main loss mechanisms of the ring current during the recovery phase of a magnetic storm. Drifting around the Earth, ring current ions encouter charge exchange with neutral hydrogen from the geocorona, which results in the generation of high energy neutrals and low energy ions. As the energetic ring current particles pass through the thermal plasma, they are scattered due to the Coulomb collision, suffering energy loss and pitch angle diffusion. FLCS occurs when the ratio of the ion’s gyration radius to the curvature radius of the magnetic field line is large enough and chaotic scattering of the particles occurs. In this study, We propose a new method of calculating the diffusion coefficients in association with FLCS, which can be applied to a more stretched magnetic configuration. With the newly calculated diffusion coefficients, we investigate the effect of FLCS on ring current particles by using the Storm-Time Ring Current Model (STRIM) and compare its role with other ring current ion loss mechanisms like charge-exchange and Coulomb collisions. The ion lifetimes associated with these different loss mechanisms are compared to gain a deeper understanding of the impact of different mechanisms in the evolution of ring current. It is found that these mechanisms exert influences on different energies and pitch angles and their impacts also vary during different phases of the magnetic storm.