Number of six-hourly global analyses across the period 1871 to 2008 recently produced as part of the Twentieth Century Reanalysis Project. The effort extends the record produced by the NCEP-NCAR Reanalysis, which begins in 1948.

A 1930s-era cooperative weather station at Granger, Utah. (Image courtesy NOAA.)

For the entire period of record, including the era that preceded ballon-borne soundings, the project is inferring the three-dimensional state of the atmosphere (including estimates of uncertainty) by using an ensemble filter to assimilate data from surface weather reports, sea surface temperature, and sea ice distribution.

The project is being led by Gilbert Compo (University of Colorado/NOAA Earth System Research Laboratory), with data contributed by international meteorological centers.

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