Electric fields deduced from plasmapause motion in IMAGE EUV images

J. Goldstein, R. A. Wolf, B. R. Sandel, P. H. Reiff


The IMAGE extreme ultraviolet (EUV) imager obtained global images of the
plasmasphere erosion of 10 July 2000, in which the nightside plasmapause moved
inward by about 2 R E during 5Ð8 UT. We use plasmapause motion to infer the
electric (E) field component tangent to the moving plasmapause; in general we
lack knowledge of the perpendicular E-field component. In the midnight-to-dawn
quadrant where the plasmapause shape is very nearly circular, the tangential
E-field component is equal to the azimuthal electric field E §j. Peak westward
E-fields of 0.6Ð1.3 mV/m were found at the plasmapause between L Å 4Ð6, an inner
magnetospheric E-field that was 25% of the solar wind E-field. The
MLT-concentration of the inferred E-field suggests that convective flows may
produce partial indentation of the nightside plasmapause (especially in the
midnight-to-dawn sector) that widens as the edges of the indentation propagate
azimuthally. 

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Geophysical Research Letters, 31, L01801, doi:10.1029/2003GL018797, 2003