Item

Abstract

In this talk we present CHAMP accelerometer data interpreted in terms of thermospheric density. In a multi-years statistical study we investigate how the air density in a latitude band of ±30° about the equator on the day and on the night side responds to external forcing. The prime driver of thermospheric density is the solar flux. For magnetically quiet days a high degree of correlation (cc>0.9) is obtained when comparing the mass density with the solar flux index. The slope of the regression line on the day side, however, is steeper by a factor of 2 than on the night side. This ratio is independent of season and solar flux level. Magnetic activity is another driver. In this case the energy input takes place at auroral latitudes. Density bulges created at high latitudes in both hemispheres propagate subsequently towards the equator. On the night side we observe a delayed response compared to the day side, which implies a later energy input in that time sector. Furthermore, we investigate which magnetic activity index is suited best to characterize the air density increase. As an example for magnetospheric input we present the thermospheric response to substorms. The presented results can be used as constraints for the improvement of atmospheric models.