A Gauge – OLR Blended Analysis of Global Daily Precipitation: A 37-Year Data Record for Hydroclimate Applications

Abstract:

Many precipitation data sets have been produced in the past two decades based on gauge measurements, satellite observations and their combinations. Their applications in hydroclimate, however, are compromised by a number of shortcomings in long-term homogeneity, quantitative accuracy, and time/space resolution. The objective of this work is to construct a homogenous analysis of daily precipitation on a 0.25^olat/lon grid over the global land for a 37-year period from 1979 to the present through combining information from CDR for the satellite observed HIRS OLR, as well as daily and monthly gauge data.

First, CPC unified daily gauge analysis is calibrated against the GPCC monthly gauge data set to correct under-estimates in the daily analysis caused by the negatively biased daily station reports. The resulting adjusted daily gauge analysis presents improved quantitative accuracy over regions with reasonable gauge coverage. A technique is then developed to derive precipitation estimates from the OLR data. PDF tables are created for the OLR and matched against those for the collocated CMORPH satellite precipitation estimates using data for 1998 to 2014. An observed HIRS OLR value is converted to precipitation through the matched OLR and precipitation PDF tables. The technique is applied to generate precipitation estimates on a 0.25^olat/lon grid over the globe for the entire HIRS OLR data period from 1979. The adjusted daily gauge analysis and the HIRS OLR-based precipitation estimates are then blended through the OI technique. The OLR precipitation estimates are used as the first guess, while the gauge data are utilized as the observation to refine the first guess.

A suite of comprehensive procedures are implemented to examine the quantitative accuracy and homogeneity of the 37-year daily precipitation data set. In particular, experiments are conducted to force the Noah land model with our new daily precipitation analysis operating under the NCEP Global Land Data Assimilation System (GLDAS). Detailed results will be reported at the GEWEX conference.

At the AGU Meetings, we will also report our recent progress on desegregating the daily precipitation analysis into three-hourly time resolution using estimates derived from GRIDSAT Climate Data Record (CDR) for geostationary TBB.