Energetic Neutral Atom Response to the Interaction Between the Magnetosphere
and the Solar Wind During the Halloween 2003 Geomagnetic Storm Period

M.E. Hill (University of Maryland, College Park, MD  20742-4111), 
D.C. Hamilton, F.M. Ipavich, G.B. Vieira, J. Meszaros, M.R. Collier and 
T.E. Moore

Measurements from the SWICS instrument on the ACE spacecraft indicate
exceedingly fast Solar wind speeds near 2000 km/s on two occasions during
the final three days of October 2003. At these times the presence of hot
plasma is indicated by He thermal speeds of about 400 km/s.  Early on 31
October, however, the thermal speed drops dramatically by an order of
magnitude, eventually reaching a minimum below 10 km/s on 1 November. The
LENA instrument aboard the IMAGE spacecraft can uniquely monitor the
energetic neutral atom (ENA) flux in the direction of the Sun.  Previous
studies have indicated the presence of an ENA component in the Solar wind
likely resulting from Solar wind charge exchange both with exospheric
neutrals and due to processes not associated with the Earth such as Solar
wind interaction with dust. During high Solar wind ram pressure time periods,
however, the dominant contributor to the neutral Solar wind flux appears to
be Solar wind charge exchange with the Earth's exosphere.  We report on the
relationship between the neutral and charged particles in the Solar wind, and
their interaction with the magneto-sphere during this active geomagnetic
period.  For instance, we investigate the possible relationship between the
broadening of the ENA angular distribution near the Sun and the variations in
the Solar wind thermal speed, as well as other pertinent features of ENA flux
and composition measurements and Solar wind observations.

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Presentation at the Yosemite Conference of Inner Magnetospheric Interactions,
3 - 6 February 2004, Yosemite, California, USA