Response of the low-latitude ionosphere-thermosphere system to high-latitude activity
Hermann Lühr and Patricia Ritter
GeoForschungsZentrum Potsdam, Potsdam
The input of energy and momentum from the magnetosphere is most efficiently coupled into the high latitude ionosphere, thermosphere. There are, however, several mechanisms which channel part of the disturbances to low and mid latitudes. Some of these mechanisms cause a prompt response, for example, the penetration electric field. Other processes require hours before the perturbation has reached the equator (e.g. travelling atmospheric disturbances). Here we will present some recent observations primarily derived from the CHAMP satellite. With its sensitive accelerometer it can measure the air density and zonal winds. During magnetic storms the thermospheric density is enhanced first at high latitudes and some hours later the bulge reaches the equator. The response time is shorter on the dayside than on the night side. None of these thermospheric responses to magnetospheric inputs are reproduced well by present-day atmospheric models.Another topic to be addressed will be the low latitude ionosphere/thermosphere response to substorm onsets. Based on a large number of substorm events the average response to this kind of disturbance was deduced. We compare ground-based and satellite observations. This allows us to distinguish between ionospheric and magnetospheric currents. There is increasing evidence for significant ionospheric currents even during the night. As a consequence of that many of the interpretations based solely on observatory data from the night side have to be reconsidered.