An East Asian Subtropical Summer Monsoon Index Defined by Moist Potential Vorticity

Based on consideration of both thermodynamic and kinetic features of the subtropical summer monsoon in East Asia,a new index is defined by the moist potential vorticity (MPV) for this monsoon.Variation features of the subtropical summer monsoon over 60 years are analyzed using National Centers for Environmental Prediction/National Center for Atmospheric Research (USA) data from 1948 to 2007.Results show that the new index can well reflect the seasonal,interannual,and interdecadal variations of the East Asian subtropical summer monsoon.Correlation analysis of the new index and precipitation data from 160 stations in China shows that in high-index years,the summer monsoon is strong,and more rain falls in eastern North China,southwestern China,and along the coast of South China and less rain falls in the Yangtze-Huaihe R.basin.In low-index years,the opposite occurs.Lastly,the new index is compared with four established monsoon indices.The new index is found to have an advantage in representing summer rainfall in the Yangtze-Huaihe R.basin.     

用湿位涡表征的东亚副热带夏季风指数

在综合考虑了东亚夏季风的热力和动力特征的基础上,利用湿位涡定义了一个新的东亚副热带夏季风指数,并利用1948—2007年NCEP/NCAR再分析资料分析了近60年来东亚副热带夏季风的变化特征。研究表明：该指数可以很好地反映东亚副热带夏季风的季节变动、年际变化、年代际变化等特征。另外,该指数与我国160个测站降水的相关分析表明：高指数年,夏季季风强,华北、西南内陆及华南沿海地区多雨,江淮地区少雨;反之,低指数年,夏季季风弱,华北、西南内陆及华南沿海地区偏旱,江淮流域偏涝。最后,通过与其它四种有代表性的指数的对比,发现本指数在指示江淮夏季降水方面具有明显的优势。