Thermal Effect of Surface Heat Source over the Tibetan Plateau on the Onset of Asian Summer Monsoon

Characteristics of the surface heating fields over the Tibetan Plateau and its adjacent areas during the onset period of Asian summer monsoon are analyzed in this paper using the NCEP/NCAP reanalysis pentadly averaged climate fields data and dekadly sensible heat and latent heat data.Effects of the sensible heating over the Tibetan Plateau on the onset of the Asian summer monsoon are discussed.Mechanisms of the Asian summer monsoon progress caused by the Plateau sensible heating and its effect on the tropical low-level west wind are revealed in detail.Results show that the longitudinal and latitudinal thermal contrasts caused by the middle latitude Plateau sensible heating trigger the onset of the Asian summer monsoon.The regional and temporal differences of the Asian summer monsoon onset bear a relation with the Plateau sensible heating region.The Plateau sensible heating has different effects on the low-level west wind in the South China Sea(SCS) before and after the onset of the SCS summer monsoon.It strengthens the low-level west wind before the onset of the monsoon but weakens the west wind after the onset.After analyzing the sensible heat in earlier and later onset years of Asian summer monsoon,it is also found that the interannual variation of the onset date of the Asian summer monsoon are related to the interannual variation of the heat source.