The exosphere/ring current interface: IMAGE observations of ENAS emitted from low
altitude

C.J. Pollock (1), A. Isaksson (1,2), D.K. Mitchell (3)

(1) Southwest Research Institute,
(2) Lulea University of Technology,
(3) Johns Hopkins University, Applied Physics Laboratory


The Medium (MENA) and High (HENA) Energy Neutral Atom imagers on NASAÕs IMAGE
satellite have been observing ring current ENA emissions since the IMAGE launch.
These emissions have often contained a component emitted from very low altitude.
This component has often appeared to be highly localized and, at times, very
bright when observed from high altitude along the IMAGE orbit, though the apparent
localization is at least partly due to highly non-isotropic (beaming) emission.
Recently, the IMAGE orbit line of apsides has precessed through low geomagnetic
latitudes, offering views of low altitude ENA emission regions from relatively low
altitude and high latitude, often sequentially from over the northern and southern
poles. From these vantage points we observe low altitude ENA emissions that are in
fact strongly peaked in pitch angle at the emission point and also strongly peaked
in Invariant Latitude distribution. The MLT distributions show a deep minimum on
the dayside for the cases studied to date. We will present these observations,
compare them with current thinking on the dynamical interaction at the
exosphere/ring current interface, and comment on the geophysical significance of
these observations.

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Presented at the 35th COSPAR Scientific Assembly, Paris, France, July 18-25, 2004.