Substorm ENA Studies

Mitchell, D. G., P. C:son Brandt, E. C. Roelof, D. C. Hamilton, C. J. Pollock,
J. M. Jahn, M.-C. Fok, M. W. Liemohn, J. U. Kozyra

Since the beginning of the IMAGE spacecraft's on-orbit science operations in
May, 2000, global images of energetic neutral atom (ENA) emissions from the
ring current have provided a new set of constraints on the processes governing
the acceleration, transport, and loss of energetic ions during geomagnetic
storms. The High Energy Neutral Atom imager (HENA) and the and Medium Energy
Neutral Atom imager (MENA) cover the relevant energy range for these emissions,
from about 1 keV to 200 keV for hydrogen and from about 80 to 250 keV for
oxygen. The images reveal the not so surprising fact while there are many
similarities among them, each storm has its own characteristics peculiar to the
details of the solar wind drivers, the orientation of the Earth's dipole, and
preceding geomagnetic activity. Although inversion techniques are only now
maturing to the extent that we can rely on them for physically meaningful
global reconstructions of the source ring current ion distributions, the ENA
images themselves provide many straightforward characteristics of the global
system without inversion, and simulations have reproduced many of the salient
features of those images.  This talk reviews many of the ring current/storm
results of the past year and a half, provides some new looks at the behavior of
energetic oxygen in geomagnetic storms, and explores the extent to which ENA
images may place constraints on the global distribution of storm time electric
fields.

_______________
To be presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, California, U.S.A., Feb. 5-8, 2002.