Abstract
Using observations of Van Allen Probes, we present a statistical study of plasmaspheric plumes in the inner magnetosphere. Plasmaspheric plumes tend to occur during the recovery phase of geomagnetic storms. Furthermore, the results imply that the occurrence rate of observed plasmaspheric plume in the inner magnetosphere is larger during stronger geomagnetic activity. This statistical result is different from the observations of the Cluster satellite with much higher L-shells in most orbital period, which suggest that the plasmaspheric plume near the magnetopause tends to be observed during moderate geomagnetic activity (Lee et al., 2016). In the following, the dynamic evolutions of plasmaspheric plumes during a moderate geomagnetic storm in February 2013 and a strong geomagnetic storm in May 2013 are simulated through group test particle simulation. It is obvious that the plasmaspheric particles drift out on open convection paths due to sunward convection during both geomagnetic storms. It seems that the outer plasmaspheric particles exhaust sooner and the plasmasphere shrinks faster during strong geomagnetic storms. As a result, the longitudinal width of the plume is narrower and the plume is limited to lower L-shells during the recovery phase of strong geomagnetic storm. The simulated evolution may provide a possible interpretation for the occurrence rates: Van Allen Probes tend to observe plumes during stronger geomagnetic storms, and the Cluster satellite with higher L-shells tends to observe plumes during moderate geomagnetic storms.
Highlights
The innermost magnetosphere is occupied by the torus of cold dense plasma known as the plasmasphere (Lemaire et al, 1998).In general, the dynamics of plasmaspheric particles are controlled by the combination of corotational and solar wind-driven convection electric fields
To explain the disparity in the occurrence rates disparity of the observed plasmaspheric plume associated with geomagnetic activity levels in different L-shells (L ≤ 6.2 in the inner magnetosphere observed by the Van Allen Probe A satellite, and L ≥ 6.2 during most of the Cluster orbital period), we run a group test particle simulation to analyze the evolution of plasmaspheric plumes during different levels of geomagnetic storms
In the present study, using density data from Van Allen Probe A, we performed a statistical analysis of plasmaspheric plumes in the inner magnetosphere
Summary
The innermost magnetosphere is occupied by the torus of cold dense plasma known as the plasmasphere (Lemaire et al, 1998). It seems that the occurrence rates of plasmaspheric plumes in the interval of -10.
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