Fluctuations of Global Surface Pressure Patterns during the Past 100 Years and Their Relation to the Asian Monsoon Part I. Northern Summer (July)

[摘要] In order to detect the fluctuations of the global circulation patterns and their relation to the Asian summer monsoon, an empirical orthogonal function (EOF) analysis was applied to the July monthly mean smoothed surface pressure data for 106 years (1871-1976) covering most of the globe. The 1st component (31% of the total variance) shows a contrasting spatial pattern between the Southern Hemisphere through the equatorial zone and the Northern Hemisphere mid-latitudes. This mode may represent the major re-distribution of the global-scale pressure patterns from the "Little Ice Age" to the recent warmer period. The 2nd component (19% of the total variance) reflects a pressure seesaw between the subtropical oceans and the Afro-Eurasian continents, which seems to be largely responsible for the strength of the Asian monsoon. These two dominant modes seem to correspond well with the long-term global-scale SST change. The 3rd component (14% of the total variance) represents a north-south (or east-west) shift of the main centers of action, and is also closely connected with the monsoon circulation. The EOF analysis of the original year-to-year data has revealed that the mode of the Southern Oscillation is also dominant as a fluctuation with periods less than 10 years, which is well correlated with the shorterperiod fluctuations of the monsoon.

[学科分类] 大气科学