Global ENA observations of the ring current: Pitch angle distributions 
and interactions with the plasmasphere during storm

P. C. Brandt, D. G. Mitchell, B. R. Sandel, J. L. Burch, E. C. Roelof 

We present global energetic neutral atom (ENA) observations of the
ring current during the geomagnetic storm on 24 May, 2000. The
observations were carried out by the ENA imager HENA onboard the IMAGE
spacecraft. Apart from the main phase of the storm the convection
through the magnetosphere was steady throughout the recovery phase,
which lasted approximately three days. ENA images below 27 keV show an
enhanced ring current at L$<$4 from midnight clockwise through noon
towards the dawn sector. At energies above 27 keV the images shows an
enhancement in the ENA emissions coming from the noon region and a
lack of ENA emissions from the duskside. Images in extreme ultraviolet
(EUV) of the plasmasphere reveal a relation between the ENA emissions
and a plasmaspheric tail. Data from the Polar and NOAA/POES satellites
suggests that the dayside ion distribution should be nearly isoptropic
and the duskside ion distribution to be strongly peaked at 90\deg
equatorial pitch angle. In attempt to explain the ENA observations we
invoke both adiabatic drifts and wave particle interactions.

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Submitted to Journal of Geophysical Research, March, 2001