The response of parameterized orographic gravity waves to rapid warming over the Tibetan Plateau

Abstract

Using the ERA-Interim reanalysis during 1979-2017, this work for the first time investigates the climatology and long-term trend of orographic gravity waves (OGWs) in the Tibetan Plateau (TP). The linkage between the trends of OGWs and the rapid warming over the TP is also studied. Climatologically, the most prominent surface wave momentum flux (SWMF) of OGWs occurs in the western and southeastern TP, while it is weak in the central TP. The SWMF is stronger in winter and spring than in autumn and summer. Overall, the mean SWMF over the TP experienced a weak decreasing trend. The decrease of SWMF mainly took place in the western and southeastern TP in spring. However, increasing trends were found in the central TP in winter. Changes of SWMF are mainly caused by the changes of horizontal wind near the surface, while buoyancy frequency and air density play a minor role. In response to the inhomogeneous warming over the TP, the surface winds were adjusted through thermal wind balance. In spring (winter), the most remarkable warming occurred in the northern (southern) TP, which reduced (enhanced) the meridional temperature gradient across the plateau, and thus led to a deceleration (acceleration) of the horizontal wind.