Impacts of the Tibetan Plateau Snow Anomaly in Winter and Spring on Precipitation in China in Spring and Summer

The climatological features of the winter snow depth over the Tibetan Plateau and the summer precipitation in China are diagnosed by use of the datasets obtained from the 78 snow observation stations and 160 rainfall stations during 1957 to 1998. Climatic effects of snow anomaly over the Tibetan Plateau on the regional summer monsoon climate in China are diagnosed and numerically simulated by use of a regional climate model (RegCM2). The SVD technique is adopted to diagnose the relationships between the prior winter and spring Plateau snow depth anomalies and the spring and summer regional precipitation in China. It is found that the snow depth anomaly especially in winter is one of factors influencing precipitation in China; however, it is perhaps not the unique one and even not the most important one. Nevertheless, it is proved that the winter snow anomaly over the Tibetan Plateau is relatively more important than the spring one for the regional precipitation in China. Results of numerical simulations show that the snow anomaly over the Plateau has evident effects on China's summer monsoon climate. The increase of both snow cover and snow depth can delay the onset and weaken the intensity of summer monsoon obviously, resulting in the decrease of precipitation in south China and the increase in the Yangtze and Huaihe River basins. The influence of the winter snow depth is more substantial than that of both the winter snow cover and the spring snow depth. The mechanism of how the Plateau snow anomaly influences the regional monsoon climate is briefly analyzed. It is found that snow anomalies over the Tibetan Plateau change the soil moisture and the surface temperature through melting process of snow at first, alter heat, moisture and radiation fluxes from the surface to the atmosphere at the meantime. Abnormal circulation conditions induced by changes of surface fluxes may affect the underlying surface properties in turn. Such a long time interaction between the wetland and the atmosphere is the key process resulting in later climate changes.