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 from the European Center for Medium-Range Weather Forecast (ECMWF), the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), and the NASA Goddard Earth Observing System (GEOS-1) reanalysis projects. The analysis focuses on the domain within 30°S-30°N, and the period is from July 1987 to December 1993. Annual-mean precipitation shows that the ECMWF overestimates the precipitation over tropical oceans as compared to the GPCP. On the other hand, the NCEP/NCAR and NASA-GEOS-1 underestimate precipitation of the Inter-Tropical Convergence Zone (ITCZ) and South Pacific Convergence Zone (SPCZ). Horizontal distributions of the difference in intra-annual and inter-annual precipitation variations between the GPCP and the three reanalysis datasets are similar to those of the difference in annual-mean precipitation. Overall, the ECMWF exhibits the highest standard deviation of precipitation over tropical oceans, followed 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.