GHRSST Reanalysis/GCOS SST-SI Intercomparisons

The two tables below list the sea surface temperature (SST) data sets that are being intercompared under the Global Climate Observing System's (GCOS) SST and Sea Ice (SI) Working Group. The goal of this group is to understand differences between different SST analyses and reconstructions with the aim of producing better, long-term SST climate data records. Also, by working in the context of the GHRSST Reanalysis effort, a second goal of linking the modern satellite-based records with the historical, primarily in situ - based records can be accomplished.

This group has chosen an initial focus on weekly, one-degree versions of the data sets as well as monthly, five-degree versions. This first milestone of this intercomparison effort is to provide each of the data sets on a common grid and in common, widely-used formats. MATLAB (V7.3) and netCDF are the primary formats. The netCDF files are COARDS/CF compliant and conform to the GHRSST format and content conventions. Please note the file names follow the proposed GHRSST Data Specification 2.0 filename convention. Note also that unlike other GHRSST files, these intercomparison data sets contain 3-dimension cubes of data, not just a single swath or grid in time.

GCOS Intercomparison Diagnostics

In addition to the data sets described above, the group is also working on a set of initial diagnostics. They have been organized into two phases:

Phase One evaluates each data set both with respect to the data set's own climatology and with respect to a common climatology (AVHRR Pathfinder V5 Q==7). Phase One diagnostics include:

-Standard deviation of anomalies in time

-Linear trend of anomalies in time (coming soon)

-Lag1 autocorrelation of anomalies in time (coming soon)

-Time series of global and hemispheric anomalies

-Time-latitude sections of anomalies (averaged across all longitudes)

Phase Two evaluates each data set with respect to every other data set. Phase Two diagnostics include:

-Map of root mean square (RMS) differences

-Map of time-averaged differences

To view browse graphics of all of these diagnostics and access the corresponding data, select Phase One or Phase Two.

To download intercomparison data dets:

The initial set of intercomparison products is listed below in two tables, one for the weekly and one for the monthly data. You can click on the netCDF or Matlab links in the table, or navigate to the following locations to access all of the data sets:

• FTP: ftp://data.nodc.noaa.gov/pub/data.nodc/GCOS
• HTTP: http://data.nodc.noaa.gov/GCOS
• OPeNDAP: Coming soon!

*Please note that the Matlab scripts available on this website are designed to illustrate the processing steps taken for each data set. They were written to cater to specific pathways on the author's computer, and are by no means complete. They will not function independently to load or parse GCOS data sets. Please direct any questions about processing or reading this data to Tess Brandon at tess.brandon@noaa.gov.

About Processing of GCOS Data Sets

The SST products used in this project were gathered from a variety of sources, and originally existed in a variety of formats. The primary task was therefore to reprocess all of these products to a standard format. Each GCOS data set contains four gridded three-dimensional variables: sea surface temperature, analysed error/standard deviation of sea surface temperature, percentage of sea ice cover, and a composite sea/land/lake/ice mask. Variables that are not available for a given data set are populated with missing values. The three dimensions that define these variables are time, latitude and longitude.

Weekly one-degree data sets are on a grid with pixel centers located at latitudes from -89.5 degrees to 89.5 degrees and longitudes from -179.5 degrees to 179.5 degrees. All data sets are forced onto the same time series, which runs from week 44 (November) of 1981 through the last week of 2007, resulting in 1366 weeks. For some products this excludes historical data that is not considered useful for the intercomparison efforts of this project. Weeks that are not available for a given product are populated with missing values. All weekly data sets were created from either weekly or daily files, and averaged in time according to the center day of each week as defined by the SST-Sea Ice Intercomparion Week Centers. For daily products, three days before and after this center day were averaged to create standard weekly averages.

Monthly five-degree data sets are on a grid with pixel centers located at latitudes from -87.5 degrees to 87.5 degrees and longitudes from -177.5 degrees to 177.5 degrees. All data sets are forced onto the same time series, which runs from January of 1981 through December of 2007, resulting in 324 months. Again, this excludes historical data from some products, and months that are not available for a given product are populated with missing values. All monthly data sets were created from either daily or monthly files, and represent calendar months (see our Calendar Date Conversion Chart). Center days for each month are defined in the file times_monthly.txt.

For ease of comparison among the data sets, a GCOS binary land mask was created at both one degree and five degreee resolution from the National Geophysical Data Center's Global Gridded 2-minute Bathymetry product. Click on the Matlab or netCDF links in the table below to download these land masks: