Precipitation water path and rainfall rate estimates over oceans using special sensor microwave imager and International Satellite Cloud Climatology Project data

The liquid/ice water paths (LWP/IWP) and the rainfall rate (RR) of precipitation systems over oceans are estimated using a combination of data from the special sensor microwave/imager (SSM/I) and the International Satellite Cloud Climatology Project (ISCCP). The retrieval scheme is based on microwave radiative transfer simulations. Collocated ISCCP cloud top temperatures are used to separate warm from cold precipitating clouds: cold precipitating clouds occur much more frequently than warm precipitating clouds and produce over 80% of the precipitation, but warm precipitating clouds are not negligible in the tropics and summer midlatitudes. SSM/I data are used to identify precipitating clouds: precipitating clouds are very rare (about 5% of all locations). Estimated IWP values, with mean about 7 mg/cm2, are quite variable, ranging from as little as 5 mg/cm2 to as much as 200 mg/cm2. The mean LWP in precipitating clouds is approximately 80 mg/cm2, occasionally reaching 1000 mg/cm2. Average RR (both cold and warm) is about 1.5 mm/hr, generally larger in the tropics than in midlatitudes. RR is larger in the northern hemispheric midlatitudes than in the southern midlatitudes. The global annual cycle of precipitation is dominated by tropical variations and is in phase with boreal seasons. The largest annual total precipitation occurs in the eastern Pacific (about 5000 mm). The subtropical precipitation minima may be underestimated because drizzle does not produce strong microwave signals.