Effect of the Asian Water Tower over the Qinghai-Tibet Plateau and the characteristics of atmospheric water circulation

Abstract

From the perspective of regional and global atmospheric moisture circulation, this paper summarizes the unique thermal and dynamic mechanisms present in the Qinghai-Tibet Plateau (QTP) and their effects on the formation of the Asian Water Tower, which provides a theoretical basis for characterizing its atmospheric moisture circulation and global influence. The results show that the mechanisms of atmospheric moisture circulation in the QTP not only reflects the interaction between westerly and monsoon moisture flow but also highlight that the QTP is a key area for global and inter-hemispheric exchanges of energy and moisture. With a comprehensive dynamic analysis of the three-dimensional structure of the wind field based on apparent heat source calculations and the stream function, we revealed that the powerful ground radiation heating and the atmospheric heat source in the QTP lead to a hollow “heat island” and “wet island” in the middle troposphere. Driven by thermal forcing, a typhoon-like self-excited feedback dynamic structure with high and low circulation systems that occur in opposite directions occur over the plateau, which drive the convergence and pumping of atmospheric vapor over the Asian Water Tower. The vector field analysis of the water vapor flux also showed that the QTP can continuously capture water vapor from tropical areas at low latitudes, and its source area extends from the subtropical Indian subcontinent to the Bay of Bengal in the tropics, and it even crosses the equator into the southern hemisphere. In view of the frequent convection and abnormal cloud precipitation over the roof of the world, the large eddy simulation further revealed the unique trigger effect of the low air density on the convective clouds. We propose that the structure of atmospheric moisture circulation under the thermal drive of the QTP can be regarded as a global atmospheric water tower. According to a comprehensive analysis of the three-dimensional dynamic and thermodynamic structures, this atmospheric moisture circulation supplies the water storage in the Asian Water Tower over the QTP. This occurs, in particular, over the plateau glaciers, snowpacks, and lakes as a reservoir with a downstream outward pipeline of rivers from the plateau. With the synergy of westerlies and monsoons, the interaction of the low-latitude ocean with plateau glaciers, lakes, rivers, and the atmosphere can construct a special system of a global ocean and air, land, and hydrological processes with the core area in the QTP. A physical picture of the land-sea-air interaction is suggested for the Asian Water Tower over the QTP.