Characteristics Of Precipitation In The Tropics And Subtropics Derived From TRMM

Precipitation can be classified into two main types, convective and stratiform. Due to different thermo-dynamics and micro-processes during the formation of precipitation, the latent heating profiles of the two rain types differ crucially. By understanding the characteristics of different types of precipitation, we can get better insight into the interrelation among atmospheric circulation, thermo-dynamical and precipitation processes, and then provide references for models. Furthermore, retrieval of rain rate from radar requires knowledge of rain types, on which drop size distribution depends. In this paper, on the basis of the comparison of mean profile for different rain types, the seasonal characteristics of precipitation frequency, conditional rain rate, storm height, vertical structures and precipitating clouds top temperature for convective and stratiform precipitation over the Tropical and Subtropical areas are analyzed. Furthermore, diurnal variations of these precipitation parameters in summer are investigated. The results obtained in the present study can be summarized as follows.1. Mean profiles of different rain types are presented. The contributions to total rain samples are about78.6%from stratiform precipitation,20.8%from convection, and only0.6%from "others". Actually, there are only sixteen of twenty four rain types whose populations exceed0.1%. The climatic characteristics of mean profiles at seasonal scale are then exposed in the Tropical belt of10°S to10°N according to over ocean or land, compared with that in the Northern Subtropics (15°N～35°N). It is found that seasonal variations of the mean profiles in the Tropics are minimal regardless of rain types, implying significant latitudinal dependent. Although the shapes of mean profiles over land and ocean resemble each other, there are still some differences between them. Meanwhile, seasonal variations of precipitation profiles over land and ocean differ crucially, mainly due to the different disabilities of underlying surface. Taking echo strength and climatic characteristics of precipitation profiles into consideration, stratiform precipitation can be reclassified as four main types while only two for both convection and "others". It is meaningful to analysis T-100-T-140subcategories for stratiform precipitation while T-200-T-240subcategories for convective precipitation as in many previous studies.2. Climatic characteristics of convective and stratiform precipitation are exposed. Convective precipitations are distributed mainly over the Intertropical Convergence Zone (ITCZ), the South Pacific Convergence Zone (SPCZ), the Asian Monsoon Region, regions between the South America and the Mid-America, and the Tropical Africa where the frequencies lie between1%and2%. But in four seasons, total area fractions of convective precipitation frequencies less than1%all exceed85%. The frequencies of stratiform precipitation are much higher than those of convective precipitation, and total area fractions of stratiform precipitation frequencies>1%are over55%during four seasons. However, frequencies of the two rain types show not only remarkable regionality, but also distinct seasonal variations. Conditional rain rates of convective precipitation range from6mm/h to14mm/h whereas those of stratiform precipitation are smaller than4mm/h. Meanwhile, rain tops of convective precipitation are higher than those of stratiform precipitation. The mean profiles of the two rain types show significant latitudinal dependency. And the seasonal variations of precipitation profiles are displayed mainly in the variations of rain tops. The frequencies and conditional rain rates of both rain types over ocean are higher than those over land, but rain tops are just the opposite. Moreover, the seasonal variations of both rain types over ocean are weaker than those over land because of the different stable states of underlying surfaces.3. Seasonal characteristics of storm height are analyzed. Storm heights of convective precipitation are relatively higher than that of stratiform precipitation, and the distributions of storm heights for stratiform precipitation are more uniform. Because of the land effect, storm heights over land are higher than that over ocean. But land effect to stratiform precipitation is not as obvious as that for convection. Generally, seasonal variations of storm heights for convective precipitation are stronger than that of stratiform precipitation. However, seasonal variations of storm heights over land (in high latitudes) are intense than that over ocean (in low latitudes). The analyses of mean profile for different storm heights indicate that near surface rain rates of convective precipitation are larger than that of stratiform precipitation. For the same storm height, near surface rain rates over ocean are intense than that over land. Clear layer structures of vertical profile for higher storm heights are also noticed. Statically, conditional rain rates and storm heights show remarkable quadratical function relationship for both convective and stratiform precipitation.4. Climatic characteristics of cloud top temperatures for precipitating clouds are investigated. Cloud top temperatures are lower than250K in regions where convective and stratiform precipitations are mainly distributed. Further analyses show that regions in which cloud top temperatures<230K (>270K) are mainly distributed over land (ocean). Cloud top temperatures also show remarkable seasonal variations. Cloud top temperatures decrease with the increment of conditional rain rates, which show obvious negative correlation. Meanwhile, negative correlation for convective precipitation is more significant than that for stratiform precipitation. The results also show that conditional rain rate is the natural exponential function versus cloud top temperatures. The analyses of vertical profiles for different cloud top temperatures show that both layer structures and land-sea dependency are more visible for higher cloud top temperatures. For the same cloud top temperature, storm height over land is higher than that over ocean, but near surface rain rate is just contrast.5. Diurnal variations of convective and stratiform precipitation in summer are discussed. Convections occur in afternoon over most land areas while in night time over ocean in summer Tropics and Subtropics. The peak time of conditional rain rate for convective precipitation does not agree with precipitation frequency very well. The largest PDF (probability density function) of peak time for conditional rain rates over land occurs in the afternoon while in the morning over ocean. The peak of storm heights and minimum clouds top temperatures over land mainly appear in afternoon and evening while in23-20LST over ocean. The diurnal variations of stratiform precipitation show similar characteristics with convective precipitation, but with a little differences of PDF among different time. Due to derived from different sensors, a shift exists between minimum clouds top temperature and peak of storm height. The diurnal variations over land are stronger than that over ocean. The diurnal variations of vertical profiles display in storm heights and near surface rain rates. Meanwhile, the diurnal variations of mean profile for convective precipitation are intense that that for stratiform precipitation.