摘要
文中利用1961～1999年NCEP/NCAR的月平均再分析资料和中国160站月降水资料,考虑蒙古中纬度地区和西太平洋副热带地区的大气环流特征定义了一个简单的东亚副热带夏季风指数,研究了该指数与夏季大气环流和中国降水变率的关系,并与其他季风指数进行了比较.结果表明:文中所定义的季风指数表现出明显的长期气候变化趋势,20世纪60～70年代以高指数为主,而80～90年代以低指数为主.该指数不仅能够较好地反映以蒙古为中心的东亚大陆热低压和西太平洋副热带高压的变化特征,还能够指示东亚副热带夏季风的强弱以及中国长江流域降水的异常变化.与西太平洋副热带高压相比,蒙古低气压变化对长江流域的雨带变动有更大影响.当该季风指数较低时,蒙古低压和西太平洋副热带高压偏弱,中国大陆对流层低层盛行异常北风,高层主要盛行异常西南风.而低层的异常北风表示了东亚中纬度地区较强的冷空气活动,这可以使长江流域梅雨锋区的辐合和上升运怂动加强,造成长江流域降水增加.
Using monthly means of the reanalyzed datasets from the NCAR/NCEP and rainfall data from 160 surface stations in China for the period 1961 - 1999 and referring to atmospheric circulations in East Asia and the western Pacific, a simple index of summer monsoon over the East Asian subtropics is defined. Relationships between the index and the variability of the atmospheric circulation and rainfall in China are examined and comparisons among different indices are made. The results show that the monsoon index in the present study displays the variability on the decadal scale. The higher-index values mainly occurred in the i960s and 1970s and the low-index values mainly occurred in the 1980s and 1990s. The index reflect the variations of both the thermal low pressure centering in Mongolia and the subtropical high in the western Pacific very well and also indicate an intensity of summer monsoon in the East Asian subtropics and an anomaly of rainfall along the valleys of the Yangtze River. Compared to the subtropical high, the low pressure exerts a greater effect on the anomalous rainfall. Corresponding to a lower index, the low pressure and the subtropical high are weaker. Meanwhile, the northerly wind anomalies prevail in the lower troposphere over the mainland of China, with the southwesterly wind anomalies in the upper troposphere. The northerly wind anomalies indicate the more frequent activities of cold air at mid latitudes of East Asia. This can cause the convergence and ascending motion to strengthen along the Mei-yu front, accompanying with the greater rainfall along the valleys.
出处
《气象学报》
CAS
CSCD
北大核心
2005年第6期933-941,共9页
Acta Meteorologica Sinica
基金
国家重点基础研究发展规划项目(2004CB418300)
国家自然科学基金课题(40305008)
中国气象局气象新技术推广项目(CMATG2005M04)
关键词
东亚副热带季风指数
大气环流
降水
East Asian subtropical monsoon index, Atmospheric circulation, Rainfall.
