Preliminary analysis of the rain profiling algorithm for TRMM precipitation radar data

This paper describes the results of preliminary analysis of the TRMM standard algorithm 2A25 which estimates the instantaneous vertical profile of rain from Precipitation Radar (PR) data. It first estimates the attenuation-corrected radar reflectivity factor from the measured reflectivity factor. The attenuation-corrected radar reflectivity factor (Z) is then converted to the rainfall rate (R) at each radar resolution cell. The major challenge of the algorithm lies in the attenuation correction that also takes into account the non-uniform beam filling effect. The attenuation correction is carried out with the combination of the Hitschfeld-Bordan method and the surface reference method. The bias in the attenuation estimate to the surface caused by the non-uniform distribution of rain is estimated from the spatial variations of the estimated total attenuations from the top of rain to the surface in the vicinity of the radar beam concerned. The Z-R relationship is also modified by the non-uniformity of rain distribution as well as rain type and height. The performance of the algorithm is analyzed with data in the initial phase of the mission. Results from such analysis are described