Influence of the Seasonal Increasing Temperature Difference between the Land and Sea Surface on the Intensity of the East Asian Summer Monsoon

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.