Carpenter, D. L., R. F. Benson, S. F. Fung, J. L. Green, M. F. Smith,
W. Calvert, R. R. Anderson, D. L. Gallagher, P. H. Reiff, B. W.
Reinisch, and W. W. L. Taylor, Radio probing of the plasmasphere,
presented at the AGU Spring Meeting, Baltimore, May 23-27, 1994.

Radio Probing of the Plasmasphere

D L Carpenter (Starlab, Stanford University, Stanford, CA  94305);
R F Benson, S F Fung, J  L Green, and M F Smith (NASA/GSFC
Greenbelt, MD  20771); W Calvert, R R Anderson (Dept. of Physics
and Astronomy, University of Iowa, Iowa City, IA  52240); D L
Gallagher (NASA/MSFC, Huntsville, AL  35812); P H Reiff (Dept.
of Space Physics and Astronomy, Rice University, Houston, TX  77251);
B W Reinisch (University of Massachusetts Lowell, Lowell, MA,
01854); W W L Taylor (Nichols Research Corp, Arlington, VA  22209)

While the existence of the plasmapause and the erosion of the
plasmasphere  during magnetically disturbed periods have been
known for 30 years, it is a  remarkable fact that there are no
observations (and in fact no physical  theory) of the plasmapause in
the process of formation. Furthermore,  observations of the
plasmasphere erosion process are limited in number and  scope.
Thus there is a significant gap in our understanding of the physical
processes involved in the substorm-associated penetration of the
middle and  low latitude magnetosphere by hot plasmas and
convection electric fields.

Radio sounding of the plasmasphere can aid our understanding
of these  processes through probing (i) the unknown process of
plasmapause  formation, (ii) the largely unknown development of
irregular density  structure at and near the plasmapause, (iii) key
aspects of the  plasmasphere erosion process, including the
apparent development of both detached and connected outlying
dense features, (iv) the persistence of  apparently eroded plasmas in
the outer afternoon-dusk magnetosphere for  extended periods, (v)
a virtually unknown disturbance-associated  phenomenon in which
as much as 2/3 of the plasma in a belt inside a newly  formed
plasmapause is dumped into the ionosphere. Along many projected
radio sounder orbits extending to ~7 Re the plasmasphere and some
outlying  dense features would be penetrated by the satellite, thus
affording  opportunities to probe plasmapause and outlier density
gradients and irregular  structure at varying probing ranges. In such
situations, as in many  others, the radio information could serve as
a valuable complement to the  data obtained from imaging the
Earth's plasma envelope by other means.