Tracking of Plasma Motions and the Global Plasma Distribution Using ENA Imaging

Jahn, J,  Brandt, P C,  Henderson, M G,  Mitchell, D,  Reeves, G D,  Pollock, C J, 
Skoug, R

The distribution and dynamics of plasma in the inner magnetosphere have long been
studied with the help of in situ satellite measurements. These studies provide
good knowledge of the local particle as well as the magnetic and electric field
environment. Correlating simultaneous satellite measurements also gives some
indication of the spatial characteristics of the plasma and its large scale
movement. However, the inference of global plasma dynamics can, depending on the
particle energy, be rather uncertain or incomplete. We have developed methods to
characterize and track large-scale plasma motions using global energetic neutral
atom (ENA) imaging from the IMAGE spacecraft. Global ENA imaging provides a
powerful tool to observe the spatial development and distribution of plasma in
the inner magnetosphere as long as care is taken in understanding the inherent
limitations of ENA imaging. We are applying our methods to the tracking of medium
energy (1.0-15 keV) and high energy (10's of keV and up) plasma movements during
substorm events as well as the morphology of the storm time ring current decay.
Events were chosen such that IMAGE was located close to the magnetic pole,
providing a good view of the inner magnetosphere while minimizing adverse viewing
effects. In general, ENA tracking from near the pole provides more reliable
results along the longitudinal direction compared to the radial direction due to
line-of-sight viewing considerations.