The response of the high-latitude thermosphere to geomagnetic activity

Abstract

The past three years have seen a wealth of new data from satellite and ground-based instrumentation describing the structure and dynamics of the thermosphere and its response to geomagnetic activity. In this review, data obtained from sampling the middle latitude and polar regions during disturbed geomagnetic periods will be surveyed for evidence of the major sources of geomagnetic energy and momentum forcing. It is not feasible to present a unique description of the storm-like phenomena induced in the thermosphere during major geomagnetic disturbances. The winter and the summer hemisphere respond differently due to the contrast in solar EUV heating and photo-ionisation in the polar regions. Geomagnetic disturbances causing similar magnetic effects may create quite different thermospheric perturbations. Certain of these latter differences may be associated with the structure of the Interplanetary Magnetic Field (IMF) before and during the event. By comparison of observational data with the predictions of numerical models, it is possible to place some quantitative limits on the total energy transferred from the solar wind via the magnetosphere and deposited in the polar ionosphere and thermosphere during some recent major events. It is also possible to assess the energy and momentum contributions of the major geophysical processes in particular regions.