On the Contribution of Plasma Sheet Bubbles to the Storm-Time Ring Current Injection

Abstract:

Plasma sheet transport is bimodal, consisting of both large-scale adiabatic convection and bursty flows. The bursty flows are associated with plasma sheet bubbles, containing lower entropy parameter PV^5/3 than their neighbors. Although bubbles are major contributors to plasma sheet transport, it is still unclear whether they play a critical role in the formation of the storm-time ring current, since bubbles are much more frequently observed tailward of 10 Re in the magnetotail than inside geosynchronous orbit. In this paper, we use RCM-E, which combines the Rice Convection Model (RCM) with the magnetic field in force balance with particle pressure, to simulate an idealized geomagnetic storm. In the simulation, random bubble injections through the high latitude boundary are superimposed on a background of large-scale enhanced convection. We use the RCM-E solutions with the test particle approach to determine the relative roles of the three mechanisms of formation of the storm-time ring current: (1) energization of particles already trapped on closed drift trajectories; (2) localized injection of plasma sheet particles in flow channels associated with bubbles; (3) large-scale cross-tail particle transport from the tail into the inner magnetosphere under enhanced convection. We will discuss the fractional contribution of each of the three sources to the storm-time ring current and provide a picture of how each mechanism works.