Latitudinal and Solar Cycle Variability of Thermosphere Composition at the Solstices

Abstract:

We analyzed column O/N2 measured by TIMED/GUVI from 2002 to 2007. GUVI column O/N2 shows consistent features in its latitudinal and solar cycle variability during the December and June solstice periods. At low solar activity, latitudinal gradients of O/N2 are small at both solstices, and they are slightly larger at the December solstice than that at the June solstice. The latitudinal gradient of O/N2 at the December solstice increases significantly with increasing solar activity, whereas it changes very little at the June solstice. Consequently, at solar maximum, column O/N2 at mid-latitudes in the northern hemisphere winter is greatly larger than that in the southern hemisphere winter. Despite considerable longitudinal variability, these features are true at different longitude sectors as well as in zonal mean column O/N2. This suggests that ionosphere winter anomaly should occur more readily in the northern hemisphere than in the southern hemisphere. Model simulations using NCAR/TIE-GCM show the same features. It is considered that high O/N2 in the winter hemisphere is due to the summer to winter inter-hemispheric circulation. However, model simulation shows that the prevailing vertical advection of O/N2 at mid-latitudes in the northern winter is not necessarily larger compared to the southern winter, especially at some longitude sectors. We will use model simulations to understand the causes of the differential latitudinal gradients of O/N2 at the solstices and their solar cycle variability.