Small-Scale Spatial Structures in the Plasmasphere

B. R. Sandel, R. A. King, W. T. Forrester, D. L. Gallagher

The Extreme Ultraviolet Imager (EUV) of the IMAGE Mission is recording our first global
images of Earth's plasmasphere. Encompassing the entire plasmasphere in a single
frame, EUV records the spatial distribution of He+ with a time resolution of
10 minutes and a spatial resolution of 0.1 RE or better. EUV measures the
brightness of 30.4-nm sunlight resonantly scattered by He+ surrounding Earth. The
30.4-nm emission from the plasmasphere is optically thin, so the measured brightness in
each resolution element is directly proportional to the He+ number density integrated
along the corresponding line of sight through the plasmasphere. Here we focus on the
behavior of small-scale structures in the plasmasphere. Movies of the plasmasphere show
how the structures form, co-rotate, and evolve with time. The most striking of these
structures include plasma tails, joined at one end to the main plasmasphere; radial
fingers extending from the main plasmasphere; and regions of reduced density within the
plasmasphere, usually in the pre-midnight sector. Energetic neutral atom imagers, auroral
imagers, and a radio sounder probe complementary aspects of the magnetosphere
thereby permitting powerful correlative analysis. Auroral emissions are also found within
the passband of EUV, so that the single data set offers information on
plasmasphere-substorm relationships.

_______________
Presented at the Fall American Geophysical Union Meeting, 
San Francisco, CA., December 15-19, 2000