Plasma Flows and Bubble Properties Associated with the Magnetic Dipolarization in Space Close to Geosynchronous Orbit

Abstract

In this paper we examine a total of 16 dipolarization events that were observed by THEMIS spacecraft in space close to geosynchronous orbit, r . For the identified events, we examine the characteristics of the plasma flows and associated bubbles as defined based on , where p is the plasma pressure and V the volume of unit magnetic flux. First, we find that the flow speed in the near-geosynchronous region is very low, mostly within a few tens of km/s, except for a very few events for which the flow can rise up to ~200 km/s but only very near the dipolarization onset time. Second, the bubble parameter, , decreases by a much smaller factor after the dipolarization onset than for the events in the farther out tail region. We suggest that the magnetic dipolarization in the near-geosynchronous region generates or is associated with only very weak plasma bubbles. Such bubbles in the near-geosynchronous region would penetrate earthward only by a small distance before they stop at an equilibrium position or drift around the Earth.