TRMM radar observations of shallow precipitation over the tropical oceans

Observations from the precipitation radar aboard the Tropical Rainfall Meas uring Mission satellite provide the first opportunity to map vertical struc ture properties of rain over the entire Tropics and subtropics. Storm heigh t histograms reveal a distinct bimodal distribution over the oceans with th e lowest mode near 2 km and the upper mode at 5 km. The low made is the dom inant feature over regions previously associated with precipitating marine stratocumulus/stratus and trade wind cumulus. In those regions a lognormal distribution fits the observed storm height distributions quite well, and a strong correlation exists between conditional mean rainfall rate and storm height. In addition, the low mode appears within the major tropical conver gence zones associated with significant precipitation, and in those regions a mixed lognormal distribution is used to separate the storm height distri bution into two parts: shallow and deep. In this exploratory analysis, the correlation between rainfall intensity and storm height is used in combinat ion with the mixed lognormal distribution to estimate that shallow precipit ation composes approximately 20% of the total precipitation over tropical o ceans during both El Nino and La Nina conditions.