Rainfall characteristics and variations in the tropics

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In the present study, the authors aimed to reveal rainfall characteristics and variations in the tropics in various time-scales using both rainfall and satellite deerived cloud data. We obrained hourly rainfall data from Malaysia and Vietnam, daily data from Indonesia, Nepal, Malaysia, Bangladesh, Vietnam, China, and monthly data from CDIAC and NCAR in USA.As a result, regional differences between coastal and inland area, and between tropics and mid-latitudes are revealed using 10-year mean hourly rainfall data in Malaysia and Japan. The relationship between diurnal variations in rainfall and wind field is also revealed in Malaysia. On a daily-scale, global distribution of recorded maximum daily precipitation is analyzed and the tropical and sub-tropical western North Pacific region including Japan in shown to bein the heaviest rainfall region of the world. On a seasonal-scale, we analyzed OLR and 5-day mean rainfall data and revealed that the tropical western North Pacific region exhibits a monsoonal climate using 12-year mean data, though it is located in a oceanic area. Also revealed is the mechanism of such monsoonal climate from a view point of air-sea interactions. Furthermore, climatological intraseasonal variations are analyzed and relationship between these variations and seasonal changes of Japan, such as Baiu and Shurin is pointed out. On a long-term time-scale, rainfall variations in Thailand are shown to be related to the SST over the eastern Pacific, those of tropical Africa and india are closely related to the SST in the lndian Ocean. Finally the rainfall variations in a entire tropics are compared with those in the basin-scale SST and close connection in regional and seasonal variations between these two parameters are confirmed. As a whole, strong influence of SST variations on tropical rainfall are emphasized. Further study is needed on the physical processes.