High-Altitude High-Latitude Electron-Density and Magnetic-Field Enhancements Observed during Magnetic Storms - Including the Storm of 17 April 2002

In addition to the spectacular remote measurements from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite [Burch, Space Sci. Rev., 2003], the Radio Plasma Imager (RPI) on IMAGE had the capability of making accurate magnetospheric local electron-density and magnetic-field determinations in addition to obtaining remote electron-density profiles [Reinisch et al., GRL, 2001; Benson et al., JGR, 2003]. These determinations were made using interleaved passive and active modes of operation of the RPI; the former were used to produce dynamic spectra and the latter to produce plasmagrams during active sounding. The plasmagrams of particular interest in this investigation were produced during the apogee (8 RE) portion of the IMAGE orbit when the RPI often operated in a high-resolution mode (300 Hz frequency steps) designed for accurate frequency measurements of sounder-stimulated plasma resonances. Here we present examples from 2001 and 2002, when the IMAGE apogee was at high latitudes, of large increases in the electron density and magnetic-field intensity (relative to quiet control conditions) during magnetic storms. During the 17 April 2002 storm, the electron density increased by about a factor of 4 and the magnetic-field intensity increased by nearly a factor of 2. During the much larger storm of 31 March 2001, the RPI data presented in Osherovich et al. [2007] indicates that the electron density increased by about a factor of 10.