Multi-scale thermospheric gravity waves observed by GOCE and CHAMP in Southern hemisphere at different Kp indices

Abstract:

We analyze accelerometer density data provided by Gravity Field and Ocean Circulation Explorer (GOCE) and Challenging Minisatellite Payload (CHAMP) in thermosphere in June–August 2004–2007 (by CHAMP, ~370 km high) and in June–August 2010–2013 (mainly by GOCE, ~260 km high). We extract multi-scale traveling atmospheric disturbances (TADs) along satellite tracks from the density variability by applying Butterworth band-pass filters. In GOCE data, we also filter out variabilities brought by satellite's eclipse transition and thruster noise. By using the least-square fitting of TAD activity when Kp indices are under 3, we extrapolated the TAD activity distribution over the Southern hemisphere at Kp=0, which is theoretically the quiet-time. The analysis reveals the features of gravity waves (GWs) hotspot distribution: (1) At GOCE altitude, in quiet-time, the hotspot of small GWs mainly focus at the Southern Andes-Antarctic peninsula region, while the hotspot of large GWs are distributed around South pole in a more isotropic way. (2) At CHAMP altitude, in quiet-time, the hotspots of GWs with different scales are mainly over the south pole, and the hotspot of large GWs is slightly shifted to the Antarctic continent (Wilkes Land), which is to the opposite direction of the Antarctic peninsula. The distributions of extrapolated quiet-time GW hotspots are consistent in some important aspects with the latest research on simulation of gravity waves in the thermosphere without geomagnetic forcing. Also, the hot spot GW distribution in different Kp indices also shows how the thermospheric GW activity is influenced by geomagnetic activity.