Global Monitoring of Precipitation on Monthly and Shorter Time Scales Utilizing Low-Orbit and Geosynchronous Satellite Observations

A satellite-based system to monitor global precipitation on monthly and shorter time scales is described. The monitoring system is based primarily on the Global Precipitation Climatology Project (GPCP) global, monthly, 2.5 degree by 2.5 degree latitude-longitude product which utilizes precipitation estimates from low-orbit microwave sensors (SSM/I) and geosynchronous IR sensors and raingauge information over land. The low-orbit microwave estimates are used to adjust or correct the geosynchronous IR estimates, thereby maximizing the utility of the more physically-based microwave estimates and the finer time sampling of the geosynchronous observations. Information from raingauges is blended into the analyses over land. This globally complete, monthly product is available from January 1986 to the present, with an extension back to January 1979 underway using non-SSM/I data. The monthly GPCP merged data product described in the previous paragraph is available a few (2-4) months after the end of the month. An analysis based solely on low-orbit microwave (SSM/1) data and the Goddard Profiling (GPROF) algorithm is used to bring the global monitoring up to real time. Anomalies from climatological means are produced from both the GPCP and GPROF fields to monitor the evolution of global precipitation, including the calculation of ENSO precipitation indices for real-time (five- day running means) climate monitoring and comparison with previous ENSO anomalies. The long-term climatology of the global precipitation field and the time and space variations thereof will be discussed, including the variations associated with the 1997- 1998 ENSO. The GPCP fields will also be compared to analyses based on the recently launched Tropical Rain Measuring Mission (TRMM). On an even shorter time scale, a new daily, 1 degree x 1 degree latitude-longitude global analysis has been developed starting in January 1997 utilizing low-orbit microwave and geosynchronous IR information using a similar method as is used to produce the monthly GPCP product. Retaining the overall small bias of the monthly product the daily product will allow greater utilization in the hydrology and other science communities.