Medium Energy Neutral Atom (MENA) emissions and the evolution of the low 
energy portion of Earth's ring current drift paths from open to closed

C.J. Pollock, J.-M. Jahn, D.J. McComas, R. Skoug, and P. Valek


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.

_______________
To be presented at the 2002 Spring A.G.U. Meeting, 
Washington, D.C., U.S.A., 28-31 May 2002