东亚夏季风指数的年际变化与东亚大气环流

THE INTER-ANNUAL VARIABILITY OF EAST ASIAN SUMMER MONSOON INDICES AND ITS ASSOCIATION WITH THE PATTERN OF GENERAL CIRCULATION OVER EAST ASIA

文中从夏季东亚热带、副热带环流系统特点出发 ,定义了能较好表征东亚夏季风环流年际变化的特征指数 ,并分析了东亚夏季风指数的年际变化与东亚大气环流及夏季中国东部降水的关系。文中定义的东亚夏季风指数既反映了夏季东亚大气环流风场的变化特征 ,也较好地反映了夏季中国东部降水的年际变化特征。此外 。

In this paper it were discussed that the characteristics of convection and zonal wind over East Asia during summer. The East Asian summer monsoon index (EASMI) was defined using the difference of anomalous wind between the (10-20°N,100-150°E) and (25-35°N,100-150°E) at 850 hPa by the averaged Jun-Aug. The phenomena have been found that the opposite variation occurred between the latitude (25-35°N) and (10-20°N) over East Asia for the anomalous zonal wind at 850 hPa. There is a seesaw variation trend for the convective intensity between the tropical monsoon trough and Meiyu front over East Asia. The interannual rainfall patterns over Eastern China during summer related to the aspects of East Asian monsoon circulation. The rainfall over Yangtze River valley was abnormal while EASMI looked stronger (weaker). Further the relationships between the EASMI and anomalous geopotential height at 500 hPa have been analyzed. The'-+-'anomalous pattern occupied over East Asia at 500 hPa height field means that the cyclone circulation strengthened over East Asian monsoon trough region and that the subtropical anticyclone over Western Pacific shifted northward than the normal during summer. Meantime there was not the blocking situation over the Sea of Okhotsk. The '+-+' anomalous pattern occupied over East Asia at 500 hPa height field means that the East Asian monsoon circulation weakened and that the subtropical anticyclone over Western Pacific shifted southward than the normal during summer. The blocking situation occupied over the Sea of Okhotsk.