The Effects of Subauroral Electric Fields on the Structure of the Plasmapause

Anderson, P.C., Johnston, W.R., Goldstein, J. 


The plasmapause is very dynamic and its structure and location are highly
dependent on the interaction between the electric field associated with Earth's
rotation and the solar-wind induced sunward convection. An increase in
magnetospheric convection causes the plasmapause to move inward and can produce
an azimuthal plasma motion in which the outer layers of the plasmasphere are
stripped away in a process known as plasmaspheric erosion. Byproducts of this
erosion include the presence of a bulge near dusk and the so-called drainage
plume. Any study or model attempting to describe the structure of the
plasmasphere and the inner magnetosphere requires detailed knowledge of the
spatial and temporal distribution of the magnetospheric electric fields. Many of
the details of plasmapause motion and structure are not well understood because
of the lack of knowledge of these electric fields, in particular the electric
fields in the inner magnetosphere on field lines that map to the subauroral
ionosphere. The subauroral electric fields can extend to very low latitudes and
can contribute substantially to the magnetospheric electric field structure,
particularly during geomagnetic storms. They are known to reduce the ionospheric
conductivity through fast chemistry and transport which produces a feedback
mechanism into the magnetosphere through coupling along magnetic field lines
further increasing the magnetospheric electric fields and their effects on the
plasmasphere. We are addressing these issues using data from the DMSP spacecraft
in the ionosphere in combination with images of the plasmasphere from the IMAGE
spacecraft. The DMSP spacecraft provide measurements of the ionospheric ion
drifts for specification of magnetospheric convection, the latitudinal profiles
of the H+ density from which the location of the ionospheric projection of the
plasmapause along the DMSP orbit track can be determined, and energetic auroral
particle precipitation from which the location of the inner edge of the electron
plasmasheet can be determined. We compare plasmapause locations derived from
DMSP measurements with those derived from IMAGE data and discuss the
plasmaspheric evolution during geomagnetic storms and the effects of the
subauroral electric fields on the plasmapause structure.

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Fall Meeting, American Geophysical Union, San Francisco, U.S.A., 
5-9 December 2005