Vertical pointing GPS receivers on four Low Earth Orbit (LEO) satellites are used to determine high altitude (topside ionosphere) total electron content (TEC) on a global scale. The TEC measurements are used to evaluate changes that occur during magnetic storms relative to a quite-time baseline, and TEC variations are correlated with both storm strength and storm phase. TEC data derived when there are independent measurements of vertical plasma drift at the magnetic equator are specifically targeted, so that correlations between changes in the vertical drift and changes in TEC are established. The research is carried out in three phases. In Phase 1 the oversatellite electron content (OSEC) is cataloged as function of satellite position and time. In Phase 2, computerized ionospheric tomography is used to invert the OSEC data, producing 2-dimensional images of the topside (including the F-region peak) plasma distribution. In Phase 3 the OSEC images are ingested into a three-dimensional ionospheric data assimilation algorithm, along with other ground-based and space-based plasma data, providing a global, three-dimensional description of the plasma distribution from the F2 ionospheric peak through the topside.
