东亚梅雨系统的天气-气候学研究

A Study of the Synoptic-Climatology of the Meiyu System in East Asia

利用1971~2000年NCEP再分析资料和中国740站的逐日地面观测资料，对东亚梅雨季的气候学进行了研究。结果表明：初夏长江流域特有的这个雨季有平均21天的长度，从6月17日开始到7月8日结束。梅雨期间降雨量达200~300mm，占夏季总降雨量的45％左右。当6月中旬东亚夏季风突然从华南向北推进到长江流域，同时印度夏季风开始在印度次大陆爆发时，中国梅雨雨季开始。这时来自南海和孟加拉湾的水汽供应显著加强，为梅雨降雨提供了非常有利的水汽条件。气候学上梅雨锋的结构主要表现为：（1）近于纬向的宽广云雨区，其中包含有强对流降水与云团；（2）锋前具有高假相当位温的高湿空气柱；（3）对流层低层跨越梅雨锋的水平温度梯度非常弱或几近消失；（4）梅雨锋区低层有一相对低的温度；（5）梅雨锋区以南为强低空偏南急流，急流以北是梅雨锋风切变线；（6）从梅雨锋区到赤道的地区是一个季风型或间接的垂直环流区。在许多方面，中国东部的梅雨锋不同于日本的梅雨锋和朝鲜的梅雨锋，因为后两者基本上是中纬度斜压结构的锋区。东亚夏季风对中国梅雨的影响要比对日本和朝鲜梅雨的影响更重要。作者对东亚梅雨系统（中国梅雨、日本Baiu和朝鲜Changma）的区域差异进行了全面的比较研究。

By using NCEP reanalysis datasets and daily surface observations at 740 stations in China, the climatological aspect of the East Asian rainy season （Meiyu） has been studied. The results have shown that this unique East Asian rainy season in early summer in the Yangtze River basin has an average duration of 21 days, starting from June 17 and ending on July 8. Its concentrated and intensive rainfall of 200 - 300 mm accounts for about 45% of total summer rainfall amount. The East Asian rainy season occurs when the East Asian summer monsoon abruptly iumps northward from South China to the Yangtze River basin in mid-June and at the same time the Indian summer monsoon sets in over the Indian Peninsula. The moisture supply coming from the South China Sea and the Bay of Bengal is greatly enhanced, thus providing a very favorable condition for Meiyu rainfall. The structure of the climatological Meiyu front is characterized by strong convective precipitation embeded in nearly zonal wide cloud zone, highly moist air column ahead of the Meiyu front of high θse, relatively lower temperature field with very weak or nearly dissipating horizontal temperature gradient across the Meiyu front at low level, strong low-level jet to the south of the Meiyu zone and wind shear line accompanying the Meiyu front, and strong upward motion in the Meiyu zone, with a monsoon type or indirect vertical circulation dominating the region equatorward from the Meiyu zone. In many ways, the Meiyu front in East China is quite different from the Baiu front in Japan and the Changma front in Korea, which are basically of mid-latitude baroclinic frontal zone. The East Asian summer monsoon has a more significant effect on the Meiyu in China than the Baiu and Changma. A comprehensive intercomparison of regional differences of the Meiyu system has been made.