Dynamics of the Plasmasphere and the Outer Radiation Belt

During geomagnetic disturbances, significant dynamics are observed in the location of the plasmapause as well as in outer radiation belt radial location and energetic particle populations. The plasmapause separates cold dense plasma in the inner magnetosphere from hot, low-density outer magnetosphere plasma, a distinction also exhibited in the characteristic plasma waves for these regions. Various wave-particle interactions inside and outside the plasmasphere are understood to be responsible for outer radiation belt particle energization and loss. We identify the plasmaspheric signature in the ionosphere--specifically the light ion trough--using DMSP spacecraft measurements. Over ten years of such observations are available from multiple DMSP satellites, coinciding with energetic particle observations by the SAMPEX spacecraft. The light ion trough is semi- automatically identified from DMSP Retarding Potential Analyzer observations of H+ densities, then mapped along magnetic field lines to the equatorial plane. Comparisons with IMAGE EUV measurements show good agreement on plasmapause locations, with indications of plasmaspheric notches and plumes identifiable in the DMSP observations. The radial movement of the plasmapause location identified by DMSP during geomagnetic disturbances correlates well with the movement of the outer radiation belt zone and SAMPEX microburst observations. We are developing an extensive database of plasmapause locations, with the goal of improving understanding of the relationship between the plasmapause location and the outer radiation belt.