EUV Imaging of Plasmapause Structures

B. R. Sandel


The Extreme Ultraviolet Imager (EUV) of the IMAGE Mission
records the distribution of He+ in the plasmasphere with
a time resolution of 10 minutes and a spatial resolution of
0.1 Re. Each image encompasses all or most of the
plasmasphere, to permit study of the structure and dynamics
of the plasmasphere in its entirety. The images reveal a
host of distinct plasmaspheric features and behaviors. Many
of these had already been inferred during the more than
three decades of investigations of the plasmasphere using
ground-based and in situ techniques, but some of them are
new and unexpected. Among the topics studied using this
technique are erosion of the plasmasphere during times of
increased convection, subsequent refilling, and connections
between plasmaspheric and ionospheric structures. EUV images
show that the plasmapause rarely conforms to the idealized
picture of a smoothly curved boundary. In contrast, the
boundary is often highly structured on length scales of 0.3-
2 Re. We focus on such structures, with particular
attention to deep indentations called voids or biteouts.
They are of special interest because of their association
with continuum kilometric radiation and because of their
possible relationship with the density cavities long known
from in-situ measurements. In addition to stimulating
interest in questions about the mechanisms by which they
form and disappear, these features serve as fiducials that
show how the cold plasma departs from corotation.

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To be presented at the 2002 Spring A.G.U. Meeting, 
Washington, D.C., U.S.A., 28-31 May 2002