Redistribution of the Stormtime Ionosphere and the Formation of a Plasmaspheric Bulge

Storm enhanced density (SED) and plasmasphere drainage plumes resulting from the erosion of the plasmasphere boundary layer by sub-auroral disturbance electric fields have been identified from both ground and space. Here we examine the source region of the erosion plumes - seen as a localized enhancement of total electron content (TEC) in the post-noon plasmasphere/ionosphere at the base of the plume. Observations suggest that this enhanced TEC results from a poleward redistribution of dusk-sector low latitude thermal plasma during the early stages of a strong geomagnetic disturbance. Ground based and low-altitude observations with GPS TEC, incoherent scatter radar, and DMSP in situ observations are combined with F-region TEC observed by the Jason and Topex satellites to provide details and a temporal history of the evolution of such events. Seen from space by IMAGE EUV magnetospheric imagery, the region of enhanced TEC appears as a pronounced brightening in the inner plasmasphere. IMAGE FUV observes the associated disturbance of the low-latitude F region as a localized enhancement of the equatorial anomalies, and provides complementary images of this inner-plasmasphere/ionosphere feature. These effects are especially pronounced over the Americas and we suggest that this results from a strengthening of the equatorial ion fountain due to the effects of undershielded (penetrating) electric fields in the vicinity of the South Atlantic magnetic anomaly. The enhanced features, seen both from the ground and from space, corotate with the Earth once they are formed. The high-TEC plasma in these regions forms a source for the dense erosion plumes which occur during strong disturbance events.