The longitudinal variations of upper thermospheric zonal winds observed by the CHAMP satellite at low and midlatitudes

In the southern hemisphere at low and middle latitudes, the local time variation of the longitudinal wind structure, including positive and negative peak locations, is almost the reverse of that in the northern hemisphere. Thus, the zonal wind patterns also show great hemispheric asymmetry. In addition, the longitudinal patterns of zonal winds in both hemispheres show seasonal variations.

The longitudinal patterns during the June solstice are significantly different from those in other seasons. These observational results are well reproduced in TIEGCM simulations. To elucidate the physical processes responsible for the observed and simulated longitudinal patterns of the zonal winds, the TIEGCM is also run for different geomagnetic field configurations.

A comparison between the TIEGCM results shows that geomagnetic field structure is the main cause of the large longitudinal variations of thermospheric zonal winds and their local time, hemispheric asymmetry, and seasonal changes at low and middle latitudes.