ENA Images of Ring Current Ion Precipitation 14-24 April 2002

R. DeMajistre, E.C. Roelof, P.C. Brandt, D.G. Mitchell


The High Energy Neutral Atom (HENA) camera on the IMAGE spacecraft images ion
precipitation from the ring current through the upward ENA albedo of the
downward ion precipitation. A newly developed ion/neutral transport theory
predicts that an appreciable fraction of the incident ions will emerge from the
exosphere (albeit at a lower energy due to inelastic collisions). These emerging
intensities register dramatically in the HENA images during perigee passes,
yielding about 6 images with excellent pixel statistics in each 2-minute
exposure. The viewing aspect during the STORMS2002 period (14-24 April) was
excellent at approximately 1500 km altitude over the southern polar cap. Almost
the entire sub-auroral precipitation region falls within the images at some time
during the passes. The emission from precipitation is also imaged at higher
altitudes when IMAGE is between about N 40 degrees - N 60 degrees magnetic
latitude, but at greatly reduced spatail resolution at the larger radial
distances of 4-7 R_E. Our analysis techniques are still in the early stages of
development, but even so, the ENA images can indicate when and where ring
current precipitation is occurring. Thus they promise a new measure of
geo-effectiveness of magnetic storm activity.

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Presentation, Fall Meeting, American Geophysical Union, San Francisco, USA, 
8-12 December 2003