The Global Precipitation Climatology Project (GPCP) was established by the World Climate Research Programme to quantify the distribution of precipitation around the globe over many years. In support of this work an international group of precipitation experts developed and produces the GPCP Version 2 monthly Satellite-Gauge (SG), Pentad, and One-Degree Daily (1DD) combined precipitation data sets. Check NCAR/UCAR’s Climate Data Guide for more information on and access to these products. A backup FTP site for the Version 2 and 1DD products is located at NASA Goddard Space Flight Center (GSFC).
The 2.5-degree Version 2 monthly suite comprises a total of 27 products with the two primary products being the monthly satellite-gauge and associated precipitation error estimates. The Version 2 product covers the period January 1979 to the present, with a delay of two to three months for data reception and processing. Version 2 supersedes all previous versions of the GPCP monthly product, including Versions 1, 1b, 1c, and V2x79. The Pentad product provides precipitation estimates on a 2.5-degree grid over the entire globe at 5-day (pentad) intervals for the period January 1979 – present. The 1DD product provides precipitation estimates on a 1-degree grid over the entire globe at 1-day (daily) for the period October 1996 – present. Both the Pentad and 1DD products are consistent with the Version 2 monthly product in the sense that the Pentad and 1DD approximately sum to the monthly SG estimate. All three precipitation products are produced by optimally merging estimates computed from microwave, infrared, and sounder data observed by the international constellation of precipitation-related satellites, and precipitation gauge analyses.
The precipitation gauge analysis used in the GPCP satellite-gauge is created by the Global Precipitation Climatology Centre; the product is available at that site and the sites listed above.
The Surface Reference Data Center (SRDC) was established in 1987 to support GPCP. Since satellites estimate rainfall through a transform of received radiance, the estimates must be verified using samples of accurate surface rainfall measurements. The SRDC, through worldwide web access, provides researchers with samples of gridded, time-space rain gauge measurements over various regions of the globe. Standard references for the combined precipitation data sets include the following:
SG: Adler, R.F., G.J. Huffman, A. Chang, R. Ferraro, P. Xie, J. Janowiak, B. Rudolf, U. Schneider, S. Curtis, D. Bolvin, A. Gruber, J. Susskind, P. Arkin, 2003: The Version 2 Global Precipitation Climatology Project (GPCP) Monthly Precipitation Analysis (1979-Present). J. Hydrometeor., 4,1147-1167.
Pentad: Xie, P., J.E. Janowiak, P.A. Arkin, R.F. Adler, A. Gruber, R.R. Ferraro, G.J. Huffman, S. Curtis, 2003: GPCP Pentad Precipitation Analyses: An Experimental Dataset Based on Gauge Observations and Satellite Estimates. J. of Climate, 16, 2197-2214.
1DD: Huffman, G.J., R.F. Adler, M. Morrissey, D.T. Bolvin, S. Curtis, R. Joyce, B McGavock, J. Susskind, 2001: Global Precipitation at One-Degree Daily Resolution from Multi-Satellite Observations. J. Hydrometeor., 2, 36-50.