JISAO data

4 by 6-degree latititude-longitude resolution anomalies of ICOADS SST, SLP, surface air temperature, winds, and cloudiness
1800 - July 2007*

For studies of climate variability over the oceans it is useful to have reasonably complete data sets. The data sets provided here are derived from the 2-degree latitude-longitude resolution International Comprehensive Ocean-Atmosphere Data Set (ICOADS), version 2 (1800-2004), and the National Centers for Environmental Prediction (NCEP) real-time marine data (2005-06). A climatology is calculated for 1950-79 (weighted by the number of observations), smoothed along latitude circles with successive 5- and 3-point running means, and then subtracted from the raw data to produce 2-degree latitude-longitude resolution anomalies. The anomalies are averaged into 4 by 6 degree latitude-longitude grid boxes, weighted by the number of observations. Zhang et al. (1997) is the appropriate reference for this data set.

* I update these files as I need them for research and some are more up-to-date than others. Type "ncdump -h filename.nc" to see what the last year and calendar month is for a specific file. The documentation in the file metadata, viewed with the ncdump command, supercedes what is on this WWW page.

There is a spurious increase in COADS SST (~0.5C) between 1941 and 1942 that is ascribed to a change from bucket to engine intake SST measurements in COADS (Folland and Parker 1995). This jump can be removed by subtracting the global-mean SST from the data, although this operation will also remove some of the global warming signal. This time series and further documentation are provided on another WWW page. Removing the global mean SST also removes a portion of the long-term trend in SST.

The NCEP real-time marine observations are processed in the same manner as the ICOADS, and they are not to be confused with the NCEP / NCAR reanalysis data. May through December 2006 are filled with missing value flags.

Data in netCDF format. All files are about 13 Mbytes in size.
At JISAO, all of these data sets are at /home/disk/muggy/data/coads/reduced_resolution/

  • Surface air temperature anomalies | number of observations
  • cloudiness anomalies | number of observations
  • SLP anomalies | number of observations
  • SST anomalies | number of observations Read the caveat above concerning SST measurements.
  • zonal wind anomalies | number of observations
  • meridional wind anomalies | number of observations


  • Folland C.K. & Parker D.E. 1995 Correction of instrumental biases in historical sea surface temperature data. Quart. J. Roy. Meteor. Soc., 121, 319-367.
  • Zhang, Y., J. M. Wallace, and D. S. Battisti, 1997: ENSO-like interdecadal variability: 1900-93. J. Climate, 10, 1004-1020.

    Data processing details
    The effect of the averaging process on the anomalies can be seen on January 1973 anomalies for 2-degree (top) and 4 by 6 degree (bottom). The color bar ranges from SST anomalies <-0.8C (>0.8C) in blue (purple).

    The strength of this data set is that it permits the user to have complete data for almost all grid points in the extratropical northern oceans. The following figure shows all of the grid boxes with complete records for all months in 1950-97.

    PostScript | JPEG
    More detailed coverage statistics for the COADS are presented at this link.


    March 2006
    Todd Mitchell ( mitchell@atmos.washington.edu )
    JISAO data