High Energy Neutral Atom Imagery of the Earth's Ring Current

Donald Mitchell and the HENA Team

The High Energy Neutral Atom imager (HENA) aboard the IMAGE spacecraft
returns an image of the energetic neutral atom (ENA) emission from the
Earth's ring current every two minutes for all orbital positions above L =
6. Early results demonstrate both the promise and the challenge presented by
these images. Several magnetic storms with Dst ranging from weak (~-30 nT)
to strong (~-300 nT) have been images, with both expected and poorly
understood results. Data from several storms (and associated substorms) will
be presented, along with interpretation based on the morphology and time
development of the events. In general, large storms produce strong, nearly
symmetric ring current emission in the 15 to 100 keV/nucleon range, whereas
weak storms appear quite assymetric, and are consistent with peak flux at
larger radial distances. Detailed modeling will be required to infer the
parent ion distriubution, since the ENA flux in any particlar image pixel is
proportional to the line integral along that line of sight of the product of
the ion flux and the cold neutral gas (primarily hydrogen geocorona)
density.

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Presented at the Seventh Huntsville Workshop, Callaway Gardens, Georgia, U.S.A. 
Oct. 30 - Nov. 3, 2000