The comparison of two merged rain gauge-satellite precipitation datasets

Two large-scale precipitation datasets, one produced by the Global Precipit ation Climatology Project (GPCP) and the other by the Climate Prediction Ce nter of the National Weather Service, and called Climate Prediction Center Merged Analysis of Precipitation (CMAP), were compared. Both datasets blend satellite and gauge estimates of precipitation. And while the latter has i ts heritage in the GPCP, different analysis procedures and some additional types of input data used by CMAP yielded different values. This study used the error characteristics of the data to assess the significance of the obs erved differences. Despite good spatial and temporal correlations between t he two fields some of the observed differences were significant at the 95% level. These were traced to the use of some different input data such as th e use by CMAP of atoll gauges in the tropical Pacific and gauges uncorrecte d for wetting evaporation and aerodynamic effects. The former impacts the t ropical ocean rain amounts and the latter is particularly noticeable in the Northern Hemisphere land areas. Also, the application of these datasets to the validation of atmospheric general circulation models is discussed.