The structure of tropical meridional circulation in summer and its regional differences and interannual variations are studied by using the July 1980—1983 ECMWF data. It is found that the tropical meridional circulation show a two-cell structure. In the lower troposphere, there are monsoon circulation in the monsoon region and Hadley circulations in the non-monsoon region; while in the upper troposphere, there is an independent circulation in both monsoon and non-monsoon regions, with its center located in the Northern Hemisphere for monsoon region and in the Southern Hemisphere for non-monsoon region. This two-cell structure always exists in normal years. However, in the abnormal year (1983), the circulation in the upper troposphere is much weaker and can hardly be recognized, and the strong vertical motion results in a one-cell meridional circulation throughout the troposphere.
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