Comparison of tropical rainfall between the observed GPCP data and the assimilation products of ECMWF, NCEP/NCAR, and NASA-GEOS-1

Combined tropical precipitation of Global Precipitation Climatology Project (GPCP) version 1 is compared with the assimilated precipitation obtained f rom the European Center for Medium-Range Weather Forecast (ECMWF), the Nati onal Centers for Environmental Prediction/National Center for Atmospheric R esearch (NCEP/NCAR), and the NASA Goddard Earth Observing System (GEOS-1) r eanalysis projects. The analysis focuses on the domain within 30 degreesS-3 0 degreesN, and the period is from July 1987 to December 1993. Annual-mean precipitation shows that the ECMWF overestimates the precipitation over tro pical oceans as compared to the GPCP. On the other hand, the NCEP/NCAR and NASA-GEOS-1 underestimate precipitation of the Inter-Tropical Convergence Z one (ITCZ) and South Pacific Convergence Zone (SPCZ). Horizontal distributi ons of the difference in intra-annual and inter-annual precipitation variat ions between the GPCP and the three reanalysis datasets are similar to thos e of the difference in annual-mean precipitation. Overall, the ECMWF exhibi ts the highest standard deviation of precipitation over tropical oceans, fo llowed by the GPCP, NASA-GEOS-1, and NCEP/NCAR. The correlation features of the area-averaged precipitation with the sea surface temperatures over the eastern equatorial Pacific Ocean are also compared among the four products , and their differences are discussed.