The merged land air and sea surface temperature data set.

      The merged land air and sea surface temperature anomaly analysis is based on data from the Global Historical Climatology Network (GHCN) of land temperatures and the Comprehensive Ocean-Atmosphere Data Set (COADS) of SST data. Temperature anomalies with respect to 1961-1990 are analyzed separately. The analyzed monthly temperature anomalies are then merged to form the global analysis.

       The analyzed SST anomalies are the extended reconstructed sea surface temperature (ERSST). The ERSST version 2 (ERSST.v2) is used for the merged analysis. That SST analysis is monthly on a 2-degree spatial grid, beginning January 1854 and updated monthly using the available in situ data updates. The ERSST.v2 anomalies are averaged to a 5-degree spatial grid to match the grid of the land data. Because of sparse observations before 1880, the ERSST analysis is heavily damped towards climatology in those years. The merged analysis is not formed before 1880.

       The GHCN data are monthly temperature anomalies on a 5-degree spatial grid. They are analyzed using the methods used in the ERSST.v2 analysis. Those methods include first analyzing the low- frequency anomaly by averaging anomalies over 15-degree spatially and 15 years temporally, where there are sufficient data for a stable average. That low-frequency anomaly is removed and the high-frequency residual anomalies are analyzed by fitting to a screened set of spatial-covariance modes. The sum of the low- and high-frequency analysis is the total anomaly analysis.

       The land and ocean analyses are performed separately and updated each month. Analyzed anomalies are then merged by weighting the land and sea analyses for each 5-degree area by the fraction of land and sea in the area. The monthly merged analysis is available beginning January 1880.

Access to the blended data set is available:
ftp://ftp.ncdc.noaa.gov/pub/data/blended/temp5d6c.v2.adj.1880.last.dat.gz

For details of the merged analysis see:
Smith, T.M., and R.W.Reynolds, 2005: A global merged land air and sea surface temperature reconstruction based on historical observations (1880-1997) (J.Climate, 18, 2021-2036.) (pdf).
GHCN:  http://lwf.ncdc.noaa.gov/cgi-bin/res40.pl?page=ghcn.html
COADS: http://www.ncdc.noaa.gov/coads/
ERSST: http://www.ncdc.noaa.gov/oa/climate/research/sst/sst.html
                ftp://ftp.ncdc.noaa.gov/pub/data/er-ghcn-sst/

Contact information:
Dick Reynolds  Richard.W.Reynolds@noaa.gov
Tom Smith  Tom.Smith@noaa.gov