Rainfall characteristics and variations in the tropics

利用降水和卫星云图资料，研究了热带地区不同时间尺度的降水特征及其变化。利用马来西亚和越南的逐时降水资料，印度尼西亚、尼泊尔、马来西亚、孟加拉国、越南和中国的逐日降水资料，以及美国CDIAC和NCAR的月降水资料，分析了马来西亚和日本10年平均逐时降水资料在沿海与内陆、热带与中纬度地区的差异。在马来西亚，降水日变化和风场的关系也被揭示出来。在逐日尺度上，分析了全球最大日降水量的分布，指出包括日本在内的热带和亚热带西北太平洋地区是全球最大降水区。在季节尺度上，我们分析了OLR和5天平均降雨量的数据，并显示，热带西北太平洋地区表现出季风气候，使用12年的平均数据，虽然它位于海洋区域。从海气相互作用的角度揭示了这种季风气候的形成机制。此外，还分析了气候的季节内变化，并指出了这些变化与日本的季节变化的关系。在长期时间尺度上，泰国的降水变化与东太平洋海温密切相关，热带非洲和印度的降水变化与印度洋海温密切相关。最后将整个热带地区的降水变化与流域尺度SST的变化进行了比较，证实了这两个参数在区域和季节变化上的密切联系。总的来说，强调了海温变化对热带降水的强烈影响。需要对物理过程进行进一步研究。

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.