The Role of the Plasmasphere in Radiation Belt

The plasmapause separates cold dense plasma in the inner magnetosphere from hot, low-density outer magnetosphere plasma. This boundary is very dynamic in response to changes in magnetospheric convection and other stormtime phenomena. The outer radiation belt is also dynamic during stormtime in terms of both radial location and energetic particle population. It is proposed that outer radiation belt particles are variously depleted and energized due to wave-particle interactions inside and outside the plasmasphere. Testing this hypothesis requires simultaneous observations of energetic particles and the plasmapause location. We derive plasmapause locations using DMSP identifications of the plasmapause signature in the ionosphere, specifically the light ion trough (LIT). This offers significantly improved temporal coverage given the continuous multiyear coverage by multiple DMSP satellites and the overlapping radiation belt observations by SAMPEX. The LIT location is semi-automatically identified from DMSP RPA observations of light ion densities, then mapped along magnetic field lines to the plasmapause. Initial comparisons show good agreement between these plasmapause locations and those obtained from IMAGE EUV observations. Case studies also show good correlations between DMSP-identified plasmapause locations and SAMPEX observations of outer radiation belt particle distributions and precipitating particle microbursts. This approach will eventually provide an extensive database of plasmapause locations, permitting us to quantify the relationship between the LIT and the plasmapause, and improve understanding of the relationship between the plasmapause location and the outer radiation belt.