GPCP Version 2.2 Combination

The Global Precipitation Climatology Project (GPCP) was established by the World Climate Research Program (WCRP) and subsequently attached to the Global Energy and Water Exchange program (GEWEX) to address the problem of quantifying the distribution of precipitation around the globe over many years. The general approach is to combine the precipitation information available from each of several sources into a final merged product, taking advantage of the strengths of each data type. The passive microwave estimates are based on Special Sensor Microwave/Imager (SSMI) and Special Sensor Microwave Imager/Sounder (SSMIS) data from the series of Defense Meteorological Satellite Program (DMSP, United States) satellites that fly in sun-synchronous low-earth orbits at 6 a.m./p.m. The infrared (IR) precipitation estimates are computed primarily from geostationary satellites (United States, Europe, Japan), and secondarily from NOAA-series polar-orbiting satellites (United States). Additional low-Earth orbit estimates include Atmospheric Infrared Sounder (AIRS data from the NASA Aqua, and Television Infrared Observation Satellite Program (TIROS) Operational Vertical Sounder (TOVS) and Outgoing Longwave Radiation (OLR) Precipitation Index (OPI) data from the NOAA series satellites. The precipitation gauge data are assembled and analyzed by the Global Precipitation Climatology Centre (GPCC) of the Deutscher Wetterdienst.

The GPCP has promoted the development of an analysis procedure for blending the various estimates together to produce the necessary global gridded precipitation fields. The currently operational procedure is described in Adler et al. (2003) and Huffman et al. (2009), and has been used to produce the GPCP Version 2.2 Combined Precipitation Data Set, covering the period January 1979 through the present (with some delay). The primary product in the Version 2.2 dataset is a combined observation-only dataset, that is, a gridded analysis based on gauge measurements and satellite estimates of precipitation. There are a total of 27 fields in the data set providing information from the individual and intermediate estimates, including estimates of RMS random error.

The data set archive consists of yearly unformatted REAL*4 binary files with ASCII headers, each of which holds 12 monthly fields. Each file occupies almost 0.5 MB. The grid on which each field of values is presented is a 2.5°x2.5° latitude--longitude (Cylindrical Equal Distance) global array of points. It is size 144x72, with X (longitude) incrementing most rapidly West to East from the Prime Meridian, and then Y (latitude) incrementing North to South. Grid edges are placed on whole- and half-degree values:

First point center = (88.75°N,1.25°E)
Second point center = (88.75°N,3.75°E)
Last point center = (88.75°S,1.25°W)

Missing values are denoted by the value -99999., and the units on the fields depend on the variable. For example, rainfall is carried as mm/day.

The standard references are:

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, E. Nelkin 2003: The Version 2 Global Precipitation Climatology Project (GPCP) Monthly Precipitation Analysis (1979-Present). J. Hydrometeor., 4,1147-1167.

Huffman, G.J, R.F. Adler, D.T. Bolvin, G. Gu 2009: Improving the Global Precipitation Record: GPCP Version 2.1. Geophys. Res. Lett., 36,L17808, doi:10.1029/2009GL040000.

The dataset curator is:
 precip data set curator
David T. Bolvin
Code 612
NASA Goddard Space Flight Center
Greenbelt, MD 20771 USA
Phone: +1 301-614-6323
Fax: +1 301-614-5492

See a list of publications citing GPCP (pdf file)
Technical Documentation
Example Software