PERFORMANCE OF SATELLITE RAINFALL ESTIMATION ALGORITHMS DURING TOGA COARE

Over 50 satellite rainfall algorithms were evaluated for a 5 degrees s quare region in the equatorial western Pacific Ocean during TOGA COARE , November 1992-February 1993. These satellite algorithms used GMS VIS /IR, AVHRR, and SSM/I data to estimate rainfall on both instantaneous and monthly timescales. Validation data came from two calibrated shipb oard Doppler radars measuring rainfall every 10 min. There was large v ariation among algorithms in the magnitude of the satellite-estimated rainfall, but the patterns of rainfall were similar among algorithm ty pes. Compared to the radar observations, most of the satellite algorit hms overestimated the amount of rain falling in the region, typically by about 30%. Patterns of monthly observed rainfall were well represen ted by the satellite algorithms, with correlation coefficients with th e observations ranging from 0.86 to 0.90 for algorithms using geostati onary data and 0.69 to 0.86 for AVHRR and SSM/I algorithms when valida ted on a 0.5 degrees grid. Patterns of instantaneous rain rates were a lso well analyzed, with correlation coefficients with the radar observ ations of 0.43-0.58 for the geostationary algorithms and 0.60-0.78 for SSM/I algorithm's. Two case studies are presented to demonstrate the capability of one TR algorithm and three microwave algorithms to estim ate instantaneous rainfall rates In the Tropics. The three microwave a lgorithms differed in their estimates of rain area but all showed grea ter ability than the IR algorithm to reproduce the spatial pattern of rainfall.