Observations and modeling of magnetic flux tube refilling of the plasmasphere at geosynchronous orbit

Abstract

AbstractThe outer plasmasphere is eroded when the strength of the convection electric field increases. Following a return of lower levels of convection, the outer plasmasphere “refills” from the ionosphere. In situ observations of the cold (~1 eV) ion number density from geosynchronous orbit indicate that within ~48 h after plasmaspheric erosion events, the number density may return to a level of ~100 cm−3, consistent with previously reported values. Current theoretical estimates of refilling rates at geosynchronous orbit are inconsistent with such rapid refilling. In order to shed light on this issue, a theoretical investigation is carried out to determine the major factors governing the refilling process. While theoretical estimates of the refilling rate reported here still fall below the observed levels by at least a factor of 2, the results of this study indicate that the morphology of the neutral atmosphere, particularly the neutral atmosphere number density, is critical in controlling the rate of refilling at geosynchronous orbit. The strength of vertical E × B drifts and horizontal neutral winds is found to play only a minor role.