Synoptic Studies of the Plasmasphere's Shape by Imaging

Bill R. Sandel, Dennis L. Gallagher, W. T. Forrester, and 
Timothy M. Bavaro


Regular imaging by the IMAGE Extreme Ultraviolet Imager reveals the
shape of the plasmasphere and the sharpness of the plasmapause over a
variety of geomagnetic conditions. Each image characterizes the
plasmasphere at a wide range of local times, and so is equivalent to
many simultaneous in-situ measurements. To take full advantage of this
new capability, new techniques in data interpretation are needed. We
have developed an approach based on binning large numbers of images
according to selection criteria such as the Kp index, Dst, and the
time derivative of Dst. Each composite image so formed represents the
time-averaged configuration of the plasmasphere under the conditions
defined by the selection criteria. To reduce errors introduced by
changing viewing perspective as IMAGE moves in its orbit, we select
images from near apogee. As a further step in compensating for changes
in viewing perspective, before adding we transform each image from the
plane of the sky as seen by EUV to the plane of the magnetic equator.
The transformation algorithm identifies the geomagnetic field line
that is tangent to each pixel's line of sight, and assigns the pixel's
brightness to the intersection of the field line with the equatorial
plane. We show examples of the composite images derived by this
procedure for a range of conditions, and compare the plasma
distributions inferred from these images to existing models and
measurements of the plasmasphere.

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Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002