Long-term variation characteristics of surface heat flux over the Tibetan Plateau before and after the onset of the South Asian summer monsoon

As the "Third Pole of the world", the thermal forcing of the Tibetan Plateau is very important for the Asian summer monsoon system; it also has great influences on the atmospheric circulation. In this paper, the European Medium Weather Forecasting Center (ECMWF) ERA Interim monthly mean reanalysis data of surface heat fluxes in the Tibetan Plateau and its surrounding areas is used. The time series of data are for March-October from 1979 to 2016 (data and method). Through the analysis of the above information, the following conclusions are reached. From March to May, the main body of the Tibetan Plateau is occupied by sensible heat flux, which increases rapidly with higher values in the west. The change of latent heat flux is smaller but increases with time. After the onset of the Asian summer monsoon, the sensible heat flux over the Tibetan Plateau decreases and latent heat flux increases rapidly. The distribution of latent heat flux shows higher values in the east and lower values in the west of the Tibetan Plateau. After the Asian summer monsoon is over, the intensities of sensible and latent heat fluxes are close to each other with higher sensible heat flux in the west and lower flux in the east. The surface sensible heat flux of the Tibetan Plateau shows a slightly downward trend, while latent heat shows an increasing trend over the past 38 years. The sensible heat flux in the western part of the Tibetan Plateau shows a weak decreasing trend, whereas the latent heat flux is increasing. In the eastern part of Tibetan Plateau, the sensible heat decreases and the latent heat shows a more obvious upward trend, which is also consistent with the climate change in the Tibetan Plateau. This is the basis for further studies that will use the data from The Third Qinghai-Xizang Plateau Atmospheric Science Experiment to analyze the change of atmospheric heat flux over the Tibetan Plateau and how the surface heating field affects the atmospheric circulation.