Dependence of plasmaspheric morphology on the electric field description during 
the recovery phase of the 17 April 2002 magnetic storm

Michael W. Liemohn, Aaron J. Ridley, Dennis L. Gallagher, Daniel M. Ober, 
Janet U. Kozyra


A comparison of how well three different electric field models can predict the
storm time plasmapause shape is conducted. The magnetic storm of 17 April 2002
is selected for this event, and plasmapause locations are extracted from images
from the EUV instrument on the Imager for Magnetopause-to-Aurora Geomagnetic
Effects (IMAGE) satellite throughout the main phase and recovery phase of the
event. The three electric field descriptions are as follows: the modified
McIlwain E5D analytical formula, the Weimer statistical compilation from
low-Earth orbit satellite data, and a self-consistent Poisson equation solution
for the subauroral potential pattern. It is found that all of the models have
certain strengths and weaknesses in predicting the plasmapause location during
this storm. The modified McIlwain model did well on the nightside but not on the
dayside because the electric fields near noon are too small (analogous to too
large of a conductance in the subauroral dayside ionosphere). The Weimer model
did well overall, but the resulting plasmapause is usually smaller than the
observed one because the electric fields are a bit too strong in the inner
magnetosphere (perhaps because of an ionosphere-magnetosphere mapping problem).
The self-consistent model is also quite good in general, but the plasmapause in
the postmidnight sector was always inward of the observed one. This is because
of too low a conductance at the location of the field-aligned currents that
close the partial ring current. It is concluded that the latter two models
provide a sufficient description of the storm time development of the
plasmaspheric morphology during this storm, with the self-consistent model being
the best choice. Another conclusion is that plasmapause locations extracted from
EUV images should be compared with peak density gradients from model results
rather than with any one isocontour of the cold plasma density itself.

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Journal of Geophysical Research, 109, A03209, doi:10.1029/2003JA010304, 2004