A Ten-Year Tropical Rainfall Climatology Based on a Composite of TRMM Products

A new climatology of tropical surface rain is described based on a composite of ten years of precipitation retrievals and analyses from the Tropical Rainfall Measuring Mission (TRMM). This TRMM Composite Climatology (TCC) consists of a combination of selected TRMM rainfall products over both land and ocean. This new climatology will be useful as a summary of surface rain estimates from TRMM (not replacing the individual products) and should be useful as a ready comparison with other non-TRMM estimates and for comparison with calculated precipitation from general circulation models. The TCC mean precipitation for each calendar month and for the annual total is determined by a simple mean of the three chosen products (slightly different combination of products over land and ocean). Over ocean areas, the three TRMM products are those based on the passive microwave (2A12), radar (2A25) and combined retrievals (2B31). Over land, the multi-satellite product (3B43) is substituted for the passive microwave product. The standard deviation (sigma) at each point among the three estimates gives a measure of dispersion, which can be used as an indicator of confidence and as an estimate of error. The mean annual precipitation over the TRMM domain of 35 degrees N to 35 degrees S in the new climatology is 2.68 mm d(-1) (ocean and land combined) with a sigma of .05 mm d(-1), or 2.0%. The ocean (land) value is 2.74 mm d(-1) (2.54) with a sigma/mean of 2.1% (5.4%). The larger dispersion (and assumed error) over land is due to the greater difficulty of satellite rain retrieval over land, especially with passive microwave techniques and especially in mountains and along coasts. The maps of sigma and sigma/mean indicate these regions of less confidence, including areas over the ocean such as the eastern Pacific Ocean. Examples of values for different latitude bands, seasonal variations, and relations of the individual inputs to the composite mean are given. Comparison with analyses from the Global Precipitation Climatology Project (GPCP) indicates lower values than GPCP for the TRMM composite in middle latitudes over the ocean and over northern Australia and India during their respective summer monsoons.