Intraseasonal Soil Moisture–Atmosphere Feedbacks on the Tibetan Plateau Circulation

Abstract

AbstractSubstantial intraseasonal precipitation variability is observed across the Tibetan Plateau (TP) during boreal summer associated with the subtropical jet location and the Silk Road pattern. Weather station data and satellite observations highlight a sensitivity of soil moisture and surface fluxes to this variability. During rain-free periods of two or more days, skin temperatures are shown to rise as the surface dries, signalling decreased evaporative fraction. Surface fluxes are further enhanced by relatively clear skies. In this study we use an atmospheric reanalysis to assess how this surface flux response across the TP influences local and remote conditions. Increased surface sensible heat flux induced by decreased soil moisture during a regional dry event leads to a deepening of the planetary boundary layer and the development of a heat low. Consistent with previous studies, heat low characteristics exhibit pronounced diurnal variability driven by anomalous daytime surface warming. For example, low-level horizontal winds are weakest during the afternoon and intensify overnight when boundary layer turbulence is minimal. The heat low favors an upper-tropospheric anticyclone that induces an upper-level Rossby wave and leads to negative upper-level temperature anomalies across southern China. The Rossby wave intensifies the upper-level cyclonic circulation across central China, while upper-level negative temperature anomalies across south China extend the west Pacific subtropical high westward. These circulation anomalies influence temperature and precipitation anomalies across much of China. The association between land–atmosphere interactions across the TP, large-scale atmospheric circulation characteristics, and precipitation in East Asia highlights the importance of intraseasonal soil moisture dynamics on the TP.