Climate Data Record for High-Resolution Global Precipitation

Thanks to the supports from the NESDIS Climate Data Record (CDR) program, projects are underway at NOAA Climate Prediction Center (CPC) to construct CDRs for two sets of gauge-satellite merged analyses of global precipitation. The first set of the CDR global precipitation analysis is that based on the CPC Morphing technique (CMORPH). Motion vectors of precipitating clouds are first derived through computing cross-correlation between two consecutive cloud images from geostationary satellites. Passive microwave (PMW) retrievals of instantaneous precipitation rates from individual low earth orbit platforms are then propagated from their respective observation times to the target analysis time. The PMW retrievals are propagated in both the forward and backward directions and the satellite-only CMORPH precipitation estimates are defined as the weighted mean of the propagated PMW retrievals from both directions. Bias correction is finally performed for the satellite-only CMORPH through PDF matching against co-located CPC unified daily gauge analysis. The bias corrected CMORPH is constructed on a 8kmx8km grid over the globe from 60S-60N in a 30-min interval covering a 16-year period from 1998 to the present and updated on a real-time basis.

The second set of the CDR precipitation product is the gauge-OLR blended (GOB) analysis of global daily precipitation. First, estimates of instantaneous precipitation rates are derived from the CDR HIRS OLR data from all available satellites. The relationship between the precipitation and the OLR is established as a function of OLR intensity, location and season through PDF matching using CMORPH and HIRS OLR data for 1998 to 2013. Estimates of daily precipitation are then computed as the arithmetic mean of those from all orbits. The OLR-based precipitation estimates are then combined with the CPC unified daily gauge analysis through the optimal interpolation (OI) technique. The OLR-based precipitation estimates are used as the first guess and the gauge analysis is used as the observations to refine the first guess. A test version of the gauge-OLR blended analysis has been produced for a 35-year period from 1979 to 2013.

As a first step of the CDR project, scripts and codes of the two processing systems are being modified to fit the requirements of CDR program. Once the modifications are completed, the systems will be transferred to NCDC for real-time processing. At the AMS meetings, details of the two systems and uptodate progress will be reported.