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.
Highlights
The Tibetan Plateau (TP) includes the highest topography in the world, with a mean elevation over 4000 m
This work investigates for the first time the changes of orographic gravity waves (OGWs) over the Tibetan Plateau (TP) and explores their relationship with the rapid warming that has been occurring in recent decades in that region
Being a subgrid-scale process, the surface wave momentum flux (SWMF) is produced by the OGW parameterization scheme of the ECMWF Integrated Forecasting System (IFS) model, which was developed by Lott and Miller (1997, i.e., LM97) using mountain wave theory [39]
Summary
The Tibetan Plateau (TP) includes the highest topography in the world, with a mean elevation over 4000 m. OGWs break break and and deposit deposit the exerting aa synoptic-scale body force known as orographic gravity wave drag (OGWD). Boos investigated the response of wintertime precipitation the forcing of orography in TP region and surroundings [15]. Since OGWs owe their existence to the interaction between the land surface and the overlying atmosphere, changes in the atmospheric fields (e.g., temperature and wind) will influence the generation of OGWs at the surface, and the OGW forcing aloft (i.e., OGWD). As studied in [28], the response of the wintertime circulation in the Northern Hemisphere to CO2 doubling in a comprehensive atmospheric general circulation model is sensitive to the strength of the parameterized OGWD. Understanding the changes of OGWs has wide implications for the simulation of the atmospheric general circulation and future projections of climate change.
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