“Downstream Effect” of Winter Snow Cover over the Eastern Tibetan Plateau on Climate Anomalies in East Asia

摘要

“Cold source” forcing effect of winter Tibetan Plateau snow cover (TPSC) on the subsequent summer atmospheric circulation anomalies over East Asia is a hot issue concerned by atmospheric scientists. Based on a statistical analysis on the mean and anomalies of snow cover (SC) depth observations at 113 stations across Tibetan Plateau, 51 stations in the eastern Tibetan Plateau (TP) were identified as the “strong signal” key stations of TPSC and the area wherein the key stations are distributed as the key area of TPSC. It was found from a comparative analysis with the winter SC areas and days of 1997-2010 from NOAA satellite products that the overall changes in winter SC at the 51 stations could not only possess a “strong signal” character but also represent the variation of whole TPSC. The distinctive differences between key area high and low SC years were found in winter (DJF)/spring (MAM) TP Q1 (apparent heat source) and Q2 (apparent water vapor sink) as well as the subsequent summer (JJA) full column water vapor flux and satellite remote sensed equivalent blackbody temperature (TBB). This paper also investigated the correlation between precursory “strong signal” character of winter SC condition in the key area and the subsequent summer water vapor transport structure in East Asia including China. Significant negative differences of winter Q1 between high and low SC years over the key area of TPSC on the height-longitude section along 32.50 N clearly show that the larger winter TPSC forcing the local atmosphere built a “cold source column” structure. This study also reveals that the summer water vapor flow confluence over the mid-lower reaches of the Yangtze River moved southwards (northwards) following the high (low) winter SC of the key area. The winter TPSC conditions were significantly correlated with the structure of subsequent summer moisture flow, i.e., the winter TPSC conditions might result in the south-north shift of the subsequent summer Meiyu system and the Western Pacific subtropical high system from their normal positions. The winter TPSC depth was closely related with the summer precipitation not only in eastern China, but also over the areas of Japan, South Korea, and Russian Far East. The above conclusions also suggest that the variations of TPSC condition and its cold source intensity might lead to the anomalous changes of East Asian climate.