Studying the Physics of the Plasmasphere and Inner Magnetosphere Using Global
Imaging

J. Goldstein (Southwest Research Institute, San Antonio, TX 78228), 
B.R. Sandel, and R.A. Wolf

IMAGE EUV routinely provides global images of the He+ plasmasphere by
detecting resonantly scattered 30.4-nm ultraviolet sunlight.  EUV images give
us the location of the plasmapause and the global equatorial He+
distribution; both of these quantities are extremely useful in constraining
models of the inner magnetospheric electric field, which has historically
been poorly known due to sparse satellite coverage. In its first four years,
EUV has yielded a great number of new science results. Features of the
plasmapause such as shoulders, notches and channels--that were not
unambiguously identified in single-point measurements--have been revealed.
Investigation of one of the first identified features, the shoulder, has
confirmed long-held ideas about the process whereby the inner magnetosphere
shields out the effects of externally applied electric fields. Observations
of plasmasphere erosion were obtained, providing opportunities to study the
timing and electric fields associated with reconnection-driven convection.
Global electric fields can be inferred from the motion of the plasmapause;
this allows study of some of the details of the erosion process, and also
opens the door to investigation of the disturbance-time inner magnetospheric
electric field. The first unambiguous observations of drainage plumes have
verified the qualitative predictions of early convection-based MHD models,
but quantitative agreement demands treatment of the physical processes that
couple the plasmasphere, ring-current/ plasmasheet, and ionosphere. The
sub-auroral polarization stream (SAPS), a ring-current/ ionospheric feedback
process, forms a narrow flow channel that focuses the effects of convection
in the premidnight and dusk MLT sectors, modifying plasmapause locations and
contributing to the formation of narrow duskside plumes. Study of hot-cold
plasma interactions shows that plasmaspheric cold plasma can foster ring
current precipitation which shows up as detached sub-auroral arcs in IMAGE
FUV data. There is a connection between drainage plumes and "storm-enhanced
density" (SED) or "tongues of ionization" in the ionosphere that implies
strong coupling between plasmasphere and ionosphere.  Images depicting
subcorotation of the plasmasphere have also indicated this strong
plasmasphere/ionosphere coupling. In summary, EUV science is in its very
early stages, but already a wealth of new understanding has resulted.  

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