Effects of gravity waves on the day‐night difference of the general circulation in the Venusian lower thermosphere

[1] We investigated generation mechanisms of the local time variation of the wind velocity in the Venusian mesosphere and thermosphere, which has been suggested from recent ground-based CO millimeter/submillimeter and CO2 10 μm observations, using our general circulation model. Our model considers the momentum transport caused by gravity waves with the gravity wave parameterization developed by Medvedev and Klaassen (2000). Our results show that atmospheric circulation distinctly changes from the dayside to the nightside. The subsolar-to-antisolar (SSAS) wind is predominant in the dayside. On the other hand, the retrograde superrotating zonal (RSZ) wind is superposed on the SSAS wind in the nightside. These characteristics are consistent with the previous observations. The westward momentum, which drives the RSZ wind in the nightside at an altitude of 110 km, is supplied by gravity waves in the 115–130 km altitude region. The downward flow that originates in the SSAS wind transports the westward momentum downward in the nightside.