Satellite Estimates of the Diurnal Cycle of Precipitation

The diurnal cycle of tropical precipitation is studied via an intercomparison of six satellite rainfall estimation methods:

1) The Convective-Stratiform Technique (CST), an infrared (IR) technique calibrated globally by rain estimates from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR); 2) CMORPH, a microwave- (MW) only technique which uses IR-derived cloud motion vectors to advect and weigh the less-frequent MW estimates; 3) The TRMM standard product 3B42, a merger of the MW and MW-calibrated (histogram-matched) global IR data; 4) MW estimates from the Special Sensor Microwave Imager (SSM/I) F13 and F15 series, available four times per day; 5) And 6) Estimates from the TRMM PR and TRMM Microwave Imager (TMI), essentially used as ground truth for this comparison, though they suffer from sampling problems over small areas and monthly time periods.

Both the diurnal cycle of rainfall and the fraction of convective rainfall (where calculable) are presented. The period of study is 2004, with special emphasis on the warm season June through August. Longer-term estimates from the PR and TMI (1998-2004) were used for a climatological comparison. Results are presented for various tropical regions, over both land and ocean. There is a large variability among the estimates, especially over land. The PR and TMI often disagree on the magnitude and phase of the fraction of convective rainfall.