Response of thermosphere density to high-latitude forcing

Abstract:

Solar wind-magnetospheric disturbances cause enhancements in the energy input to the high-latitude upper atmosphere through particle precipitation and Joule heating. As the upper atmosphere is heated and expanded during geomagnetically disturbed periods, the neutral density in the thermosphere increases at a fixed altitude. Conversely, the thermosphere contracts during the recovery phase of the disturbance, resulting in a decrease of the density. The main objectives of this study are (1) to determine the morphology of the global thermospheric density response to high-latitude forcing, and (2) to determine the recovery speed of the thermosphere density after geomagnetic disturbances. For (1), we use thermospheric density data measured by the Challenging Minisatellite Payload (CHAMP) satellite during 2000-2010. It is demonstrated that the density enhancement during disturbed periods occurs first in the dayside cusp region, and the density at other regions slowly follows it. The reverse process is observed when geomagnetic activity ceases; the density enhancement in the cusp region fades away first, then the global density slowly goes back to the quiet level. For (2), we analyze EISCAT Svalbard radar and Tromso UHF radar data to estimate thermospheric densities during the recovery phase of geomagnetic disturbances. We attempt to determine the time constant for the density recovery both inside and outside the cusp region.