Magnetic Storms as seen by IMAGE

J.-M. Jahn (1) , P. C. Brandt (2), R. Demajistre (2), M. G. Henderson (3), D. J. McComas (1), 
D. G. Mitchell (2), J. D. Perez (4), C. J. Pollock (1), G. D. Reeves (3), E. C. Roelof (2), 
R. Skoug (3), M. F. Thomsen (3)

(1) Southwest Research Institute, San Antonio, USA (jjahn@swri.edu; Fax:+1-210-520-9935)
(2) Johns Hopkins University - Applied Physics Lab, Laurel, USA 
(3) Los Alamos National Laboratory, Los Alamos, USA 
(4) Auburn University, Auburn, USA 


Since its launch in March 2000, the NASA IMAGE spacecraft has observed a large
variety of magnetic storms ranging from small events up to several "superstorms".
Using energetic neutral atoms (ENAs) as tracers for the charged particle dynamics,
the Medium and High Energy Neutral Atom Imagers (MENA and HENA, respectively)
imaged these storms covering the whole inner magnetosphere simultaneously.
Depending on the energy range, MENA and HENA measurements give insight into
dynamics controlled by a varying combination of corotation, convection and magnetic
drifts. We are presenting IMAGE ENA observations illustrating the storm time ring
current configuration, effects of substorm injections during storms, and first results
on the composition of ENA measurements during storms. Time periods will include
the events of 4-6 October 2000, 12 August 2000 and 31 March 2001. The storm time
ring current exhibits a stronger dependence on interplanetary magnetic field (IMF)
conditions than on storm phase. In particular, the ring current is distinctly asymmetric
for southward IMF conditions even in the recovery phase, whereas it can become
symmetric already during the main phase if the IMF turns northward. Examples of
the role of substorms during geomagnetic storms include the 4-6 October 2000 storm,
where a series of "sawtooth injections" during moderately southward IMF conditions
shows repeated injection of fresh plasma sheet material into what appears to be a partial,
or untrapped, ring current. In connection with the storm-substorm relationship we
will also present first results on ENA composition measurements, showing bursts of
oxygen ENA's associated with substorm injections during storms.

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Geophysical Research Abstracts, 4, EGS02-A-06424, European Geophysical Society, 2002
Presented at the EGS Meeting, Nice, France, April 2002.