A new system has been developed to produce real-time analyses of daily precipitation on a 0.1 degree latitude/longitude grid over South Asia (70E-110E; 5N-35N). The system takes 4 kinds of observation-based data sets as inputs. These are the GTS gauge observations, estimates derived from satellite observations of IR (GPI), SSM/I and AMSU-B.

A 2-step algorithm is applied to define the daily analysis by merging the 4 kinds of input data sets. First, to reduce the random error inherent in the individual inputs, the 3 satellite estimates (GPI, SSM/I and AMSU-B) are combined linearly through the Maximum Likelihood Estimation method, in which the weighting coefficients are inversely proportional to the individual error variance. The combined satellite estimates are then blended with the gauge observations through the method of Reynolds (1988), in which the combined analysis and the gauge data are used to determine the 'shape' and the magnitude of the precipitation fields, respectively. Preliminary examinations have shown substantial improvements of the merged analysis of daily precipitation compared to the individual data sources.

The system has been put into operation at the Climate Prediction Center (CPC) of NOAA in support of weather and flood monitoring activities at USAID and USGS. Its products, in binary data and GIF graphic files, are available on a quasi real-time basis through anonymous ftp.