Abstract: The characteristics of precipitation diurnal variations in spring and summer are investigated based on the TRMM satellite data from 1998 to 2012. The South China Sea (SCS) and surrounding areas are divided into four main regions: the South China region, Indo-China peninsula region, Malaysia region, and the SCS region. The results show that: First, in low latitude regions of the two hemispheres, the precipitation has opposite variation phases in spring and summer. In spring, the precipitation mainly occurs in Malaysia region and its surrounding area. However, in summer, the precipitation is more distributed over the SCS region and its surrounding area while the precipitation over Malaysia region is small. The Philippine islands, Indo-China peninsula, and the South China region present land pattern of diurnal variation, which means the precipitation maximum occurs after noon. For Malaysia region, the precipitation maximum occurs at night. Second, the diurnal difference is related to land-sea difference. In general, the precipitation is larger at night than that in the daytime over land area while it is larger in the daytime than at night over sea area. Moreover, the diurnal difference is generally more significant over sea area than over land area. The diurnal difference is most significant over the SCS in both spring and summer. In summer, it is also significant over the South China region. From spring to summer, the diurnal difference reduces in Malaysia and the SCS regions while it ascends in the rest two regions. Third, in summer, the Indo-China peninsula and the Philippines present similar patterns of diurnal variations. Their precipitation maximums occur at around T 17:00-20:00 in both areas, which is earlier than in spring. Meanwhile, the high precipitation period of the SCS region occurs earlier in summer than in spring. In both seasons, the diurnal variation patterns of the four regions are similar. The diurnal variations over the South China region and the Indo-China peninsula region present single peak pattern. In Malaysia region, the diurnal variation is relatively gentle. Fourth, based on the data from 1998 to 2012, in spring, the interannual variations of the occurring time of precipitation minimums are not significant in the Indo-China peninsula and the SCS regions while the variation in Malaysia region is relatively large. The interannual variations of the occurring time of precipitation maximums are little in Indo-China peninsula region. For Malaysia region, the variation has become smaller since 2005 and stayed small from 2005 to 2012. From spring to summer, the interannual variations of the occurring time of precipitation maximum become more significant over the Indo-China peninsula region and less significant over the SCS region. The interannual variations of the occurring time of precipitation maximum are similar in both seasons. Last, the seasonal difference can well illustrate the precipitation variation from spring to summer. After the burst of summer monsoon over the SCS region, the precipitation variation decreases slightly around Malaysia and equator areas while increases over South China, SCS and Indo-China peninsula regions, especially over the Philippine islands. What is noteworthy is that in South China region, the Xisha Islands and their surrounding sea show a negative seasonal difference, which means its precipitation decreases after the burst of monsoon, while the major part of this region has positive seasonal difference.

Key words: TRMM, spring and summer precipitation, diurnal variations, difference, the South China Sea (SCS)