Winter SST anomalies, a COADS derivative

A dataset of winter sea surface temperature (SST) anomalies has been derived from the Comprehensive Ocean-Atmosphere Data Set (COADS), using the 1-by-1 deg. SST product from the period 1960-1997.

You may download the data here (netcdf, gzip'ed). The winter season has here been defined as the period November-April (inclusive). The first winter is Nov. 60-Apr 61, and the last (37th) winter is Nov. 96-Apr 97.

The data processing, which is described in Section 2 in Melsom et al., 2001 (gzip'ed pdf file), requires a minimum data coverage in time. If certain criteria are not met for a grid cell, the data are discarded for this cell. However, data are also extrapolated from "wet" cells, within a limit radius. Cells which are based on extrapolation may be discarded by multiplication of the variable sst_mask(x,y). For a brief introduction to the present data processing, and some examples, look here, and a comparison with a remote sensing product is provided here.

The two main variables in this data set are (in Fortran lingo, i.e., with reversed sequence of variable arguments):
• sst_anom(x,y,w) which contains the anomalies in space [x and y, nodes defined by the variables lon(x) and lat(y), respectively] and time [w, winters defined by time(w)]
• sst_climatology(x,y,m) which contains the offsets from the overall winter means of the various winter months [m, months defined by month(m)], e.g. if sst_climatology(x,y,1)=0.5, the November SST climatology is 0.5 deg. warmer than the winter climatology for this particular grid cell.

Below is a printout of the netcdf file header:

netcdf coads_sst_winter {
dimensions:
        lon = 360 ;
        lat = 180 ;
        month = 6 ;
        time = UNLIMITED ; // (37 currently)
variables:
        int time(time) ;
                time:long_name = "Time" ;
                time:units = "year" ;
        int month(month) ;
                month:long_name = "Month" ;
                month:units = "month" ;
                month:first_month = 11 ;
                month:first_month_txt = "first winter month (1: January, ..., 12: December)" ;
                month:last_month = 4 ;
                month:last_month_txt = "last winter month (1: January, ..., 12: December)" ;
        float lon(lon) ;
                lon:long_name = "Longitude" ;
                lon:units = "degrees_east" ;
        float lat(lat) ;
                lat:long_name = "Latitude" ;
                lat:units = "degrees_north" ;
        int sst_mask(lat, lon) ;
                sst_mask:long_name = "Sea surface temperature, climatology mask" ;
                sst_mask:mask_txt = "=1: wet node (as defined by the global attribute\"fraction_clim\"), =0: filled node" ;
        float sst_climatology(month, lat, lon) ;
                sst_climatology:long_name = "Sea surface temperature anomaly, monthly climatology" ;
                sst_climatology:missing_value = -1.e+10f ;
                sst_climatology:units = "deg. Celsius" ;
        float sst_anom(time, lat, lon) ;
                sst_anom:long_name = "Sea surface temperature, winter anomaly by years" ;
                sst_anom:missing_value = -1.e+10f ;
                sst_anom:units = "deg. Celsius" ;

// global attributes:
                :title = "Comprehensive Ocean-Atmosphere Data Set (COADS) Winter SST" ;
                :source = "NOAA-CIRES Climate Diagnostics Center" ;
                :method = "Winter SSTs, filled using SOR for Laplacian" ;
                :author = "Dr. Arne Melsom, Norwegian Meteorological Institute" ;
                :email = "arne.melsom@dnmi.no" ;
                :grid = -259.5f, -89.5f, 1.f, 1.f, 0.f, 0.f ;
                :fraction_clim = 0.5f ;
                :fraction_clim_txt = "fraction of occurence in all winter months, required for inclusion in seasonal cycle fields" ;
                :fraction_one = 0.8f ;
                :fraction_one_txt = "fraction of occurence in at least one winter month,required in initial land-sea gridding (see fulfil2_txt)" ;
                :fraction_min = 0.7f ;
                :fraction_min_txt = "fraction of occurence in at least one winter month, the grid will ultimately be wet if close to a truly wet grid for (at least) one winter month for all years (see radius_txt)" ;
                :fulfil2 = 1 ;
                :fulfil2_txt = "flag for requiring one (=0) or both (=1) of the criteria associated with fraction_clim/fraction_one to be satisfied for the initial land-sea grid" ;
                :radius = 1 ;
                :radius_txt = "maximum distance in grids to a truly wet grid from a dry, potentially wet, grid (see fraction_min_txt)" ;
                :radius_clim = 3 ;
                :radius_clim_txt = "maximum distance in grids to a non-masked climatology node grid from a dry, potentially wet, grid (see fraction_min_txt)" ;
                :eliminate = 1 ;
                :eliminate_txt = "no. of years to exclude from computation of seasonal cycle, as determined by to high intraseasonal variability" ;
                :scans = 51 ;
                :scans_txt = "maximum no. of iterations in Laplacian SOR for filling dry domain" ;
                :relax_coeff = 1.6f ;
                :relax_coeff_txt = "SOR coefficient (should be between 1.2 and 2.0)" ;
                :SOR_cnvrgnce = 1.e-04f ;
                :SOR_cnvrgnce_txt = "Number used in SOR convergence test (about 4 orders of magnitude down from data)" ;
}