Variations of Surface Heat Fluxes over the Tibetan Plateau before and after the Onset of the South Asian Summer Monsoon during 1979-2016

As the Third Pole of the World, the Tibetan Plateau (TP) is an important thermal forcing to the South Asian summer monsoon (ASM) and even the global atmospheric circulation. In this paper, surface heat fluxes from the ERA-Interim reanalysis data during March-October of 1979-2016 in the TP and its surrounding areas are examined and analyzed. The results are as follows. (1) From March to May (before the ASM onset), the main body of the TP is dominated by sensible heat flux, which increases rapidly with high (low) values in the west (east), while the change of latent heat flux is small but it increases with time. (2) From June to August (after the ASM onset), sensible heat flux over the TP decreases, while latent heat flux increases rapidly with high (low) values in the east (west). (3) From September to October (after the ASM withdrawal), sensible and latent heat fluxes are comparable to each other in strength, again with high (low) sensible heat flux in the west (east). (4) During 1979-2016, surface sensible heat flux in the whole TP shows a slightly downward trend, while latent heat flux shows an increasing trend. Specifically, in the western TP, sensible (latent) heat flux shows a weak decreasing (an increasing) trend; while in the eastern TP, sensible (latent) heat flux decreases (increases obviously). These variations are consistent with the observed wanning and moistening in the TP region. The above results are useful for further analysis of the change of atmospheric heat sources and surface heat fluxes over the TP based on the data from the Third Tibetan Plateau Atmospheric Science Experiment (TIPEX-III).