http://eagle1.umd.edu/GPCP_ICDR/GPCPmonthlyV2.3.pdf

The gridded data are a blend of the CRUTEM4 land-surface air temperature dataset and the HadSST3 sea-surface temperature (SST) dataset. The dataset is presented as an ensemble of 100 dataset realisations that sample the distribution of uncertainty in the global temperature record given current understanding of non-climatic factors affecting near-surface temperature observations.

Surface marine observational records from ships, buoys, and other platform types are processed and binned creating monthly global and regional grids of the observations along with processing statistics such as stand deviation and number of obs. Data starts back as far as 1662 and some grids are update to the present.

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The NCEP-DOE Reanalysis 2 project is using a state-of-the-art analysis/forecast system to perform data assimilation using past data from 1979 through near present. Data is output on 17 pressure levels and on single level grids. Data is output 4x daily and is also available as daily and monthly. Climatologies are provided for select variables.

Data is from NCEP initialized reanalysis (4x/day). It consists of most variables interpolated to pressure surfaces from model (sigma) surfaces.

Data is from NCEP initialized analysis (2x/day). It consists of most variables interpolated to pressure surfaces from model (sigma) surfaces.

The GODAS dataset is a real-time ocean analysis and a reanalysis. It is used for monitoring, retrospective analysis as well as for providing oceanic initial conditions for the CFS. Both temperature and synthetic salinity profiles are assimilated in a 3DVAR scheme designed by Derber and Rosati (1989). 40 vertical levels are in the model together with 1x1 data values (enhanced in resolution to 1/3x1/3 degrees latitude within 10 degrees of the equator). The data is provided at 1/3x1/3 degrees for all latitudes.

The NARR dataset is an extension of the NCEP Global Reanalysis which is run over the North American Region. The NARR model uses the very high
resolution NCEP Eta Model (32km/45 layer) together with the Regional Data Assimilation System (RDAS) which, significantly, assimilates precipitation
along with other variables. Data is output 4-8 times daily. Daily and Monthly values are available. The datasets starts in 1979.