Observations of small geomagnetic storms by the High Energy Neutral Atom
Camera on the IMAGE spacecraft

Donald Mitchell and the HENA Team

The High Energy Neutral Atom imager (HENA) on the IMAGE spacecraft has
imaged a number of magnetic storms, both great and small.  This presentation
will focus on the small storms, which from the perspective of energetic
neutral atom (ENA) images turn out to be more dynamic than large storms.
The primary reason for this is that with a weaker global electric field, the
drift paths and injection histories of ions in the HENA energy range (~15 to
60 keV/nucleon, in practical terms) are quite assymetric and time variable,
whereas in large storms with deeper injections they tend to be more stable.
Small storms, with relatively large radius ring current concentrations,
usually place ions in this energy range on open drift paths (in actuality,
the ions change energy continuously in the changing electric amd magnetic
fields they drift through).  What can be seen is the differential drift at
different ion energies, so that injections at one time and place quickly
separate in the images of ENA at different energies.  The possibilities for
deriving new insights into storm dynamics will be discussed.

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Presented at the Fall American Geophysical Union Meeting, 
San Francisco, CA., December 15-19, 2000