Sea surface temperature and precipitation clouds for tropical oceans

The sea surface temperature (SST) effect on convective cloud system (CCS) and precipitation are investigated using data measured by the Tropical Rainfall Measuring Mission (TRMM). The measurements from the Visible and Infrared Scanner (VIRS) are used to identify cloudiness and cloud top temperature by the Clouds and Earth's Radiant Energy System (CERES) project. The cloud water temperature is retrieved from the Microwave Imager (TMI) measurements using the microwave radiation transfer model of Lin et al. (1998). The precipitation data are the TMI hydrometeror profile data acquired from the GES Distributed Active Archive Center.

This study focuses over 30S-30N region for 1998. The SST ranges from 290K to 305K in this region. The brightness temperatures (11 micrometer channel of VIRS) of 245K and 273 K are chosen to identify CCSs and to separate cold and warm rains, respectively. Although two thirds of the sky have clouds, the CCSs cover only about 13%, statistically. Most of the CCSs occur at SST between 302K and 304K where the coverages reach as high as 45%. The effective radius of CCSs range from tens to thousands km. Smaller CCSs with high raincell ratio (>50%) usually have the highest rainfall rate and amount.

The average chance of cold rains (4%) are twice as those of warm rains (2%), but cold rains could reach as high as 8% for the area with SST between 302 K and 304K. The average cold cloud rainfall rate(2.71mm/h) is 4.5 times as that of warm cloud rainfall rate(0.62 mm/h), but the rain amount of cold clouds is nine times as those of warm clouds. More than 90% of rainfall amount are produced with SST between 300K to 304K. Rainfall rate increases with SST and peaks at 304K, but such high SST area are limited. The correlation coefficient between SST and rainfall rate is higher than 0.96 for the area with SST between 290K and 305K. Cloud top temperatures (T_top) decrease and cloud base temperatures (T_base) increase with SST.The correlation coefficients are approximately -0.86 (SST vs T_top), 0.99 (SST vs T_base), and 0.97 (SST vs thickness) for the studied region. Further more, the correlation coefficient between cloud thickness and rainfall rate is higher than 0.93.