Influence of Anomalous Heat Sources over the Tibetan Plateau on the Anomalous Activities of the 1999 East Asian Summer Monsoon
青藏高原热源异常对1999年东亚夏季风异常活动的影响

In the context of the anomalous heat sources over the Tibetan Plateau in 1999, we discuss its influence on the anomalous activities of the East Asian summer monsoon and analyze the formation reason of anomalous heat sources. The results show, that the establishment of heat sources over the Plateau was very late and the intensity of heat sources was very weak in spring and summer. This made the low-level inflow to the Plateau become weak and the ascending motion be depressed. And the convergence around the Plateau was smaller and the monsoonal meridional cells became weaker than normal. The southwesterlies on the southern and southeastern flanks of the Plateau were depressed, which caused the late onset and weak northward advance of the summer monsoon in the eastern China during 1999. The further exploration to the formation cause of the anomalous heat sources indicate that the abnormal weakening of sensible heat flux, which can cause anomalous evolution of land surface characteristics, is the main cause of the anomalous heal sources. The decrease amplitude of the Plateau's snow cover is smaller than normal in spring and summer, which made the increase of land surface temperature be slow and the temperature lower. As a result, the sensible heat flux was weaker than long-term mean in spring and summer, which caused the anomalous heat sources.