Trend In The Atmospheric Heat Source Over The Tibetan Plateau And Its Influence On Interdecadal Variation Of Summer Precipitation In China During The Past30Years

In terms of linear trend estimate, correlation analysis, empirical orthogonal function analysis and partial regression analysis, the trend in the atmospheric heat source over the central and eastern Tibetan Plateau (CE-TP) is quantitatively estimated using historical observations at71meteorological stations, three reanalysis datasets from1980-2008, and two satellite radiation datasets from1984-2007, and the impacts of the thermal forcing of the CE-TP during spring on changes in summer rainfall over China are investigated. The chief conclusions are as follows:(1) The weakened trend in sensible heat (SH) flux over the CE-TP continues, and the most significant trend occurs in spring, induced mainly by decelerated surface wind speeds. The ground-air temperature difference shows a notable increasing trend over the last5years.(2) Trends in net radiation flux of the atmospheric column over the CE-TP, evaluated by two satellite radiation datasets, are clearly different. Trends in the atmospheric heat source calculated by the three reanalysis datasets are not completely consistent, and even show opposite signals. Results from the two datasets both show a weakening of the heat source but the magnitude of one is significantly stronger, whereas an increase is indicated by the other data. Therefore, it is challenging to accurately calculate the trend in the atmospheric heat source over the CE-TP, particularly from the estimates of the reanalysis datasets.(3) The sensible heat (SH) flux and snow depth over the TP both decreased over this time period, although the trend was more significant in SH and it can characterize the heat conditions in TP better. The similarity between patterns of precipitation trends over China and corresponding patterns of partial regression coefficients on the leading mode of spring SH change over the TP demonstrates the distinct contribution of changes in TP SH during spring. Enhanced precipitation in South China was accompanied by increases in heavy rainfall, precipitation intensity, and the frequency of precipitation events, while reduced precipitation in North China and Northeast China was primarily associated with decreases in the frequency of precipitation events. Further analysis reveals that the reductions in SH over the TP have weakened the monsoon circulation and postponed the seasonal reversal of the land-sea thermal contrast in East Asia.