Morphology of Magnetospheric Storm-Time Medium Energy Neutral Atom (MENA) Emissions

C.J. Pollock (1), J.-M. Jahn (1), D.J. McComas (1), J. Perez (2), R Skoug (3), 
P. Valek (1)

(1) Southwest Research Institute (cpollock@swri.edu/1-210-520-9935)  
(2) Auburn University (perez@physics.auburn.edu/334-844-4613) 
(3) Los Alamos National Laboraotry (rskoug@lanl.gov/505-665-3332)


Storm-time images from the MENA imager on NASA's IMAGE satellite are presented.
Previous observations have shown a large degree of asymmetry in the MLT
distributions of storm-time ENA emissions, particularly during the main phase. In
contrast, during the late storm recovery the distributions have been observed to 
become more symmetric. These observations have been interpreted to indicate large
scale plasma loss at the day side magnetopause due to enhanced convection during
storm main phase and subsequent trapping and and ring current symmeterization later
in the recovery phase. We have examined the MENA images from numerous storms, along 
with the corresponding Dst signatures. The objectives are to identify how typical
this transition from asymmetric to symmetric distributions is, and to identify any
association between the transition on the one hand, and a break in the Dst recovery
profile from steep to more gradual on the other. Such an association would indicate
that the transition in Dst recovery rates is due to a transition in ring current 
drift paths from open to closed.

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