Remote Imaging of Storm-Phase Ion Heating

The MENA (Medium Energy Neutral Atom) instrument onboard the IMAGE spacecraft allows for global imaging of the magnetosphere in neutral atoms with energies ranging from 1 to 60 keV. Using known charge exchange cross sections and the properties of the instrument, the measured neutral atom energy spectra along each line-of-sight of the instrument can be converted into ion energy spectra. By fitting the ion energy spectra with a Maxwellian velocity distribution, global maps of the ion temperature during periods of elevated activity can be generated [Scime et al., 2002]. In this work, we combine remote ion temperature imaging using neutral atoms with an image processing algorithm that accounts for variations in the viewing geometry due to orbital precession and seasonal variations to sum images from eight large geomagnetic storms. Storm time images were separated into four intervals, pre-storm, main phase, early recovery, and late recovery. To distinguish between storms with differing convection electric field strengths, the storms were sorted by cross polar cap potential drops obtained from DMSP satellite measurements of ion flows. We find that storms with strong polar cap potential drops (i.e. < - 80 kV) exhibit more ion heating during the main phase and throughout the recovery than storms with more mild potential drops (i.e. ~ -50 kV). Ion heating clearly localized to the ring current region is also more apparent in those storms with stronger polar cap potential drops.