青藏高原冬春季积雪异常对中国春夏季降水的影响

利用1956年12月～1998年12月共42a，青藏高原及其附近地区78个积雪观测站的雪深和我国160站月降水的距平资料，分析了其气候特征，并用SVD方法分析了冬春季积雪异常与春夏季我国降水异常的关系。用区域气候模式RegCM2模拟了青藏高原积雪异常的气候效应并检验了诊断分析的结果。分析表明，雪深异常，尤其是冬季雪深异常是影响中国降水的一个因子。研究证明，高原冬季雪深异常对后期中国区域降水的影响比春季雪深异常的影响更为重要。数值模拟的结果表明，高原雪深和雪盖的正异常推迟了东亚夏季风的爆发日期，减弱了季风强度，造成华南和华北降水减少，而长江和淮河流域降水增加。冬季雪深异常比冬季雪盖异常和春季雪深异常对降水的影响更为显著。机理分析指出，高原及其邻近地区的积雪异常首先通过融雪改变土壤湿度和地表温度，从而改变了地面到大气的热量、水汽和辐射通量。由此所引起的大气环流变化又反过来影响下垫面的特征和通量输送。在湿土壤和大气之间，这样一种长时间的相互作用是造成后期气候变化的关键过程。与干土壤和大气的相互作用过程有本质差别。

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.