Rapid response of the plasmasphere to changes in the solar wind and IMF:  Global 
plasmapause measurements by IMAGE EUV, and MSM simulation

J. Goldstein (1), R. A. Wolf (1), B. R. Sandel (2), T. Forrester (2), 
D. Gallagher (3), and P. H. Reiff (1), R. Spiro (1)

(1) Dept. of Physics and Astronomy, Rice University, Houston, TX 77005 USA
(2) Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 USA
(3) NASA Marshall Space Flight Center, Huntsville, AL 35812, USA 


Images obtained by the extreme ultraviolet (EUV) instrument on the IMAGE 
satellite very often show a well-defined and identifiable plasmapause; dynamic 
changes in the shape and location of this plasmapause can be tracked by EUV with 
10-minute time resolution.  For some time, it has been established that the 
plasmapause moves in response to changes in the global magnetospheric convection 
field, which in turn is driven by solar wind dynamic pressure and interplanetary 
magnetic field (IMF) orientation.  A handful of time histories recorded by EUV 
show the plasmapause moving radially inward or outward.  Comparison of the 
EUV-observed plasmapause time development with IMF orientation in these cases 
shows that the plasmapause responds rapidly (within 25 to 30 minutes) to sudden 
changes in the IMF Bz polarity.  A change to southward Bz enhances 
magnetospheric convection, causing visible inward motion of the nightside 
plasmapause.  A change to northward Bz seems to trigger an overshielding 
condition, producing outward motion of the nightside plasmapause.  In general 
the plasmapause motion (inward and outward) seems to be concentrated most 
strongly in the post-midnight sector, with a lesser concentration at pre-noon 
MLT.  This spatial character is consistent with simulation results of the Rice 
Magnetospheric Specification Model (MSM).  The overall picture, from both 
observation and simulation, is that the plasmapause location is very responsive 
to changes in the solar wind and IMF conditions.

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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