Influence Of Snow Over The Tibetan Plateau In Winter And Spring On Summer Rainfall Distribution In China

By using the methods of diagnostic analysis and numerical simulation, the influence of snow over the Tibetan Plateau (TP) in winter and spring on precipitation distribution in summer in China is studied and its possible mechanism is analyzed. The paper also discusses the possible reason of snow's increasing over the TP in winter and spring.Main results are as follows:(1) Discovering that snow over the TP in winter and spring is increasing in decadal scales, especially snow in spring has an abrupt increase. The atmospheric heat sources over the TP and its neighboring areas take on a persistent downtrend in spring and summer during the past 50 years, especially in the last 20 years. Snow in winter and spring has notable negative correlation with the atmospheric heat source in spring and summer over the TP and its neighboring areas. The increase of the former has important contribution to the decrease of the latter.(2) Statistic correlations of observation data find that snow over the TP has remarkable positive correlation with precipitation in the middle and lower Yangtze River, and reversed correlation in South China and North China not only in inter-annual scales but also in inter-decadal scales .(3) The simulations of surface rainfall and temperature are distinctly improved after adopting envelope topography.(4) In the sensitive experiments of more snow over the TP than normal by using climate model, the simulated precipitation pattern is consistent with the observed, namely, more rainfall occurs in the middle and lower Yangtze River; Less rainfall presents in South China and North China. The results accord with the pattern of"southern flood and northern drought".(5) Both the numerical simulation and data analysis in this paper show that East Asian winter and summer monsoons have marked reversed correlation in the inter-decade scale and snow over the TP in winter and spring plays an important role. Stronger East Asian winter monsoon can bring out more snow over the TP; and then more snow over the TP could lead to stronger East Asian winter monsoon and subsequently weaker East Asian and South Asian summer monsoons.(6) Discovering possible impacting mechanism of snow over the TP in winter and summer with monsoon and rainfall distribution in summer in China. In the early stage of snow, surface reflectivity is dominant; After snow is melted,"Moist Soil"contributes to the prolonged influence process of snow on weather and climate. The reduction of absorbed solar radiation due to the increased reflectivity, the increasement of absorbed heat as snow is melted, and the long-term interaction between moist soil and atmosphere change the heat source of the TP, which are the main impacting mechanism of snow over the TP in monsoon and rainfall distribution in China.(7) Presenting the reasonable explaining of"southern flood and northern drought". Both data analysis and numerical simulation show that, much snow over the TP is one of reasons of"southern flood and northern drought"in East China.(8) Possible reasons of more snow over the TP in winter and spring are also investigated. The enhanced winter monsoon at 850hPa caused by the strengthen of Mongolia High, influences the Bay of Bengal (BOB), and triggers cyclonic circulation in the lower troposphere; At 500hPa, shear is formed between the eastern wind in south of anti- cyclone at Mongolia (i.e., Mongolia High) and the cyclonic circulation in south of TP; The vertical ascending is reinforced in the large extent area of east TP; The water vapor entering the TP increases in spring.