本文通过对比几种不同的东亚夏季风强度指数，发现东亚及附近地区海陆表面温度的变化与东亚夏季风强度有密切联系。在此基础上，根据强、弱夏季风年东亚表面温度差值的逐候数据做EOF分析，结果发现：第一模态可以揭示从春到夏的季节转换，中国东部陆地增温相对较快，而西太平洋及孟加拉湾海温增温较慢，季节转换提前，有利于夏季风偏强；第二模态则反映了春季中高纬度地区增温快、中低纬增温慢的情形，有利于夏季风增强。在5月份两种模态的综合作用显示：陆地较冷、海洋较暖，夏季陆地的快速增温、海洋增温慢，有利于夏季风增强。将上述影响因素引入到改进的东亚夏季风强度指数中，修正后的指数可以反映东亚地区5月到夏季的海陆增温特点以及季节转换的早晚，并更好地描述了季风区中、高纬度的热力差异，合理地解释夏季风强度与西北太平洋副高及低空急流的关系，因此新指数能够更好地反映全国范围内夏季降水的特点。%Through comparison of several different East Asian summer monsoon intensity indices, it is found that surface temperature changes and the intensity of the East Asian summer monsoon are closely related. Using the Empirical Orthogonal Function (EOF) of pentad data for the differences in surface temperature between strong and weak East Asian summer monsoon years, the first mode reveals that, in the transition from spring to summer, rapid warming of the land in eastern China and slow warming of the sea in the western Pacific and the Bay of Bengal is conducive to enhanced monsoon. The second mode reveals that, in spring, rapid warming in the middle–high latitudes and slow warming in the middle–low latitudes also favors enhanced monsoon. Therefore, the colder land and warmer ocean in May are favorable to rapid summer warming and slow ocean warming. The impact of this feature is used to develop an improved East Asian summer monsoon intensity index—one that is more conducive to reflecting the characteristics of summer rainfall across the country. The new index can reflect the effects of different warming characteristics of sea and land on the relationship between the intensity of the summer monsoon and the Northwest Pacific subtropical high and low-level jet.
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