Systematic Differences of Rainfall Estimates in TRMM 3G68

Characteristics of systematic differences beetween TRMM Precipitation Radar (PR) and Microwave Imager (TMI) rain estimates derived from TRMM-3G68 version 5 datasets are analysed and the possible factors contributing to these differences are identified. Our study suggests that the distribution of rainfall differences with respect to their convective percentages brings out their characteristics under different convective/stratiform regimes, which are classified subjectively by utilizing TMI and PR convective percentages, rain cover percentages, Visible Infrared Scanner (VIRS) brightness temperature and the differrence between TMI and PR rain estimates in 0.5 x 0.5 degree grids. The result shows that at low (high) TMI convective percentages and high (low) PR convective percentages, representing the formative (mature) stage of convection, PR rain estimates are found to be larger (smaller) than TMI. Significantly large differences in rain estimates, with overestimation of rain by TMI, occur when PR convective percentage is < 60% and TMI convective percentage is > 30%.