THE DECADAL RELATIONSHIP BETWEEN ATMOSPHERIC HEAT SOURCE OF WINTER AND SPRING SNOW OVER TIBETAN PLATEAU AND RAINFALL IN EAST CHINA

By adopting reverse computation method, the calculation and analysis from NCEP/NCAR daily reanalysis data from 1960 to 2004 show that, atmospheric heat sources over Tibetan Plateau (TP) and its neighboring areas take on a persistent downtrend in spring and summer during the foregone 50 years, especially latest 20 years. While snow depth at 50 stations over TP in winter and spring represents an increase, especially the snow depth in spring exhibits a sharp increase after the late 1970s. A close negative correlation exists between snow cover and atmospheric heat source over TP and its neighboring areas by SVD method, namely if there is more snow on TP, then weaker atmospheric heat source over TP. The SVD analysis between atmospheric heat source over TP in spring and summer and rainfall at 160 stations indicates that, the former has negative correlation with precipitation in the middle and lower Yangtze River, and has positive correlation with South China and North China; Also from the results of SVD analysis, atmospheric heat source over TP in winter and spring and rainfall at the same 160 stations indicates that, the former has marked positive correlation with precipitation in the middle and lower Yangtze River, and reversed correlation in South China and North China. In the decadal years scale, the atmospheric heat source and winter and spring snow over TP has close correlation with decadal precipitation pattern shift(southern flood and northern drought) in East China. In the end of the article, it is discussed the mechanism how atmospheric heat source over Tibetan Plateau influence rainfall in East China. The weakening of atmospheric heat source over TP in winter and spring can reduce the heat difference between ocean and continent, leading to weaker East Asian summer monsoon, which brings less water vapor to North China and more water vapor to Yangtze River valley; Simultaneously the weakening of atmospheric heat source over TP render the position of subtropical high more westward and rainbelt to last more time, which cause more rainfall in Yangtze River valley and less rainfall in North China, namely southern flood and northern drought in latest 20 years. The increasing of snow over TP brings about the weakening of atmospheric heat source over TP. Possible physical mechanism is as follows. In the early stage of snow, surface reflectivity is dominant. After snow melts, “Moist Soil” contributes to the prolonged influence process of snow on weather and climate. The reduction of absorbing solar radiation due to the increased reflectivity, the more needing heat when snow melts, and the long-term interaction between moist soil and atmosphere change the heat source of the TP, which is the main influencing mechanism of snow on atmospheric heat source over TP.