The characteristics of tropical precipitation profiles as inferred from satellite radar measurements

Abstract

In this study, we analyzed the vertical precipitation profiles in the tropics derived from radar onboard the Tropical Rainfall Measuring Mission satellite. For a given rain type, principal component analysis was done to all the profiles that have similar rainfall rate at 2 km altitude. It is found that the first principal component can explain more than 80% of the variations in the profiles, and the reconstructed first principal components closely resemble the ensemble mean. It is therefore concluded that the mean profiles are representative of the typical pattern of the vertical precipitation structure. The mean profiles for deep convections and stratiform rains are then derived and analyzed for the entire year of 1998 in the tropical belt of 15°S to 15°N. The results show that on a logarithm scale the slopes of the profiles are approximately constants if the profiles are divided vertically into 3 or 4 layers. The difference in slopes among layers may reflect the difference of dominant microphysical processes by which the precipitating hydrometeors either grow or evaporate. The difference between rain profiles between over ocean and over land, and the variation of rain profiles with latitudes are also investigated in this study. As one of the applications of the typical profiles to satellite remote sensing, we calculated the brightness temperature -rainfall rate relations using profiles derived in this study and those provided by previous investigators. It is demonstrated that the brightness temperatures resulted from vertical profiles of previous investigators generally agree, to some extent, with those resulting from the profiles of this study. However, some significant discrepancies exist over some rainfall rate ranges and for high microwave frequencies. It is expected that using the profiles of this study will lead to the improvement of satellite rain retrievals because they are derived from a much larger set of observational data, and are more representative of precipitations in the tropics. ©2001, Meteorological Society of Japan.