高原夏季风指数的定义及其特征分析

基于1958~2002年ECMWF再分析资料,我国160个台站降水和气温资料,从夏季高原季风环流系统特点出发,定义了能较好表征高原夏季风环流变化的特征指数,分析了高原夏季风年际、年代际变化特征,并揭示了高原夏季风强弱异常时的环流特征及其与中国夏季降水和气温的关系,主要结论为:(1)用6~8月600hPa (27.5~30°N,80~100°E)范围内平均的西风分量距平与(35~37.5°N,80~100°E)范围内平均的东风分量距平差定义了高原夏季风指数(PM I)。该指数计算简单,意义清楚,代表性好。(2)1958~2002年高原夏季风整体呈增强趋势,在20世纪60年代中期之前是高原夏季风的强盛期,之后是高原夏季风弱期,在80年代以后又转为季风强期。(3)高原夏季风与中国夏季降水和气温相关很好。将该指数与之前汤懋苍定义的指数进行性能综合比较后,发现该指数对川渝地区的夏季降水及气温有更好的指示意义。 

The Definition of Plateau Summer Monsoon Index and Analysis on Its Characteristics

Based on ECMWF monthly reanalysis information, monthly rainfall and air temperature data from 160 primary stations in China from 1958 to 2002, it were discussed that the characteristics of convection and zonal wind over plateau during summer and the inter-annual variation and inter-decadal variation of plateau summer monsoon.Further, we define a new plateau summer monsoon index and analyze the relationship between the plateau summer monsoon index (PMI) and summer climate in China.The main conclusions are:(1) The plateau summer monsoon index (PMI) was defined using the difference of anomalous wind between the (27.5~30°N, 80~100°E) and (35~37.5°N, 80~100°E) at 600hPa by the averaged from Jun to Aug.The phenomena have been found that the opposite variation occurred between the latitude (27.5~30°N) and (35~37.5°N) over plateau for the anomalous zonal wind at 600hPa.The PMI corresponds with summer climate over China in distinctive patterns. (2) The plateau summer monsoon had an increase trend from 1958 to 2002.Before the middle 1960s the plateau summer monsoon is in its powerful stage, afterwards it weakend until the end of 1980's and became strong again.The remarkable inter-annual variation and inter-decadal variation of the plateau summer monsoon occur throughout 45 years. (3) There existed obviously positive correlation between the plateau summer monsoon and the precipitation in the west of Xinjiang, the east and south of plateau, the northwest of Yunnan, the east of Sichuan and Chongqing Basin, and the downstream of Yangtze River in summer, and obviously negative correlation between the plateau summer monsoon and the precipitation in the west of Sichuan and Chongqing Basin, Gansu, Hetao, North China, and South China.Similarly, there existed obviously positive correlation between the plateau summer monsoon and the air temperature in the north of Xinjiang, the north of Qinghai, the northeast of plateau, Hetao, Gansu, and South China in summer, and obviously negative correlation in the west of Xinjiang, the east of Sichuan and Chongqing Basin, and the downstream of Yangtze River.In summary, it indicates that the plateau summer monsoon has an important impact on the intermediate deck aerosphere circulation climate. (4) Comparison of the overall performance of the new plateau summer monsoon index and the one defined by Tang (1984) shows that the plateau summer monsoon index has a better instruction significance to the summer precipitation and the temperature of Sichuan and Chongqing Basin.