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Ann. Geophys., 16, 1380-1391, 1998
www.ann-geophys.net/16/1380/1998/
© European Geosciences Union 1998
The thermospheric effects of a rapid polar cap expansion
D. W. Idenden
School of Mathematics and Statistics, The Hicks Building, University of Sheffield, Sheffield, S3 7RH, UK
Abstract. In a previous publication we used results
from a coupled thermosphere-ionosphere-plasmasphere model to illustrate a new
mechanism for the formation of a large-scale patch of ionisation arising from a
rapid polar cap expansion. Here we describe the thermospheric response to that
polar cap expansion, and to the ionospheric structure produced. The response is
dominated by the energy and momentum input at the dayside throat during the
expansion phase itself. These inputs give rise to a large-scale travelling
atmospheric disturbance (TAD) that propagates both antisunward across the polar
cap and equatorward at speeds much greater than both the ion drifts and the
neutral winds. We concentrate only on the initially poleward travelling
disturbance. The disturbance is manifested in the neutral temperature and wind
fields, the height of the pressure level surfaces and in the neutral density at
fixed heights. The thermospheric effects caused by the ionospheric structure
produced during the expansion are hard to discern due to the dominating effects
of the TAD.
Key words. Ionosphere (ionosphere ยท atmosphere
interaction; modeling and forecasting; plasma convection).
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