Imaging the Dynamic Magnetosphere: Quantitative ENA Tracking During
Substorms and Storms

Jahn, J.-M., P. C. Brandt, M. G. Henderson, D. Mitchell, C. J. Pollock,
G. D. Reeves, R. Skoug, M. F. Thomsen, and P. Valek

Bulk particle motions in the inner magnetosphere during substorms and
storms have long been studied with the help of single and
multi-satellite measurements. These studies provide good knowledge of
the local particle as well as magnetic and electric field environment.
However, the inference of the global plasma distribution and dynamics
can be rather uncertain.

We are developing methods to quantify large-scale particle motions
using global energetic neutral atom (ENA) imaging from the MENA and
HENA detectors. Specifically, we explore the level of analysis possible
prior to subjecting ENA measurements to image inversion techniques.
Global ENA imaging provides a powerful tool to observe the spatial
development and distribution of plasma in the inner magnetosphere.
Under the right circumstances ENA observations can be used to track the
particle motion and quantify its spatio-temporal development. We are
presenting tracking results from several substorm events and 2000 and
2001. 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. We track the earthward movement of
plasma during the expansion phase as well as the local time extent of
medium energy plasma (which is subject to the competition between
convection, corotation, and magnetic drifts) and the gradient curvature
drift of high energy plasma (10's of keV and up). We discuss the
ramifications of using direct ENA tracking as opposed to the tracking
of inverted plasma populations. The application of this tracking
technique to other geospace events like ring current decay is also
discussed briefly.

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