Gravity wave-induced variability of the middle thermosphere

Abstract

Contemporary theory, modeling, and first-principles simulations indicate that dissipation of gravity waves (GW) plays an important role in modifying the mean circulation, thermal structure, and composition of the thermosphere. GW can propagate into the thermosphere from various sources in the lower atmosphere, deposit energy, and momentum into the thermosphere, and thereby modify its mean circulation, thermal structure and composition. However, measurements that verify or constrain predictions of GW propagation well into the thermosphere, especially on a global basis, are extremely limited. In this paper total mass densities and cross-track winds between 230 and 280 km derived from accelerometer measurements on the Gravity Field and Ocean Circulation Earth Explorer (GOCE) satellite between November 2009 and October 2013 are used to reveal the global morphology of horizontal structures between 128 km and 640 km, which are assumed to mainly reflect the presence of GW. The zonal-mean RMS variability at these scales is quantified in terms of seasonal-latitudinal dependences and dawn-dusk differences, which are interpreted in terms of current theoretical and modeling results. Little evidence is found for any longitude variability that can be attributed to specific source regions, except at high latitudes where polar/auroral sources and magnetic control dominate and near the Andes and the Antarctic Peninsula during local winter.