DATA ACQUISITION

Observed Data:
  1. GOSTAplus
  2. Arctic and Southern Ocean Sea Ice Concentration, NSIDC
  3. SMMR

Models:
  1. Canadian Global Coupled Model, CGCM1
  2. Atmosphere Ocean Model, GISS
  3. Hadley Centre's Second Generation GCM, HadCM2
  4. Atmosphere Ocean Model R15, GFDL
  5. IOS Arctic Ice-Ocean Model

With the exception of GOSTA, all model and observed data were downloaded from the web. This section will contain brief file descriptions, and any special instructions on converting to different file formats. The web addresses for the complete online documentation will also be included for reference.

  1. GOSTAplus
    Online documentation:
    http://podaac.jpl.nasa.gov/cdrom/gostaplus_hdf/order.htm

    This CD-ROM contains a data set called GISST2.2, which contains monthly global ice concentration grid data.
    Temporal Coverage:
    Monthly ice concentration values from January 1903 to December 1994.
    Grid Spacing, Dimensions:
    Each grid cell is 1° by 1°. The dimensions of the entire grid are 360x180.
    Grid Coordinates:
    The longitudes range from 179.5° W to 179.5° E, and the latitudes range from 89.5° N to 89.5° S. There is no separate file containing a grid of latitudes and longitudes. The coordinates were instead calculated using a FORTRAN routine.
    Ice Concentration:
    Ice concentrations vary from 0 to 10, as integers. A value of -32768 is LAND - no separate land mask is necessary.
    Notes:
    The GOSTAplus CD-ROM is distributed by the Physical Oceanography Distributed Active Archive Center at the Jet Propulsion Laboratory (JPL) and the UK Meteorological Office. Note that monthly data is only unique from year to year from 1949 onwards. Forty-six (46) ice concentration files are on the CD-ROM, each containing two years of data.
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  2. Arctic and Southern Ocean Sea Ice Concentration, NSIDC
    Online documentation:
    http://nsidc.org/NSIDC/CATALOG/ENTRIES/G00799.html

    This data set was provided by the National Snow and Ice Data Center (NSIDC), located at the University of Colorado, Boulder, CO. This data set will often simply be called "NSIDC" in this web site.

    There are four files available for downloading:
    • aricecon.dat - Arctic ice concentration data
    • aricesrc.dat - source of arctic ice data
    • arctic.grd - Grid cell data
    • arctic.crd - Grid cell lat/lon coordinates
    Please refer to the online documentation for details on these files.
    Temporal Coverage:
    Monthly ice concentration values from January 1901 to August 1995

    Note that NSIDC documentation recommends using pre-1953 data with care as this data is either climatology or interpolated data.
    Grid Spacing, Dimensions:
    The dimensions of the Arctic grid are 80x58. The grid is a cylindrical projection of a standard 1° grid. The approximate grid spacing is 1° by 1°.
    Grid Coordinates:
    All grid cell lat/lon coordinates are available in the file arctic.crd. The online documentation contains a list of reference coordinates.
    Ice Concentration:
    The ice concentration data is located in aricecon.dat. The data are arranged sequentially from January 1901 to August 1995. Ice concentration values are ASCII characters representing the number of tenths of ice coverage in each grid area, ranging from 0 to 9. A '*' represents total (ten/tenths) ice coverage. A '.' indicates that the grid point lies over land.

    The file arctic.grd contains land mask data. If a grid cell is completely over land, the grid cell is assigned a value of -1. For all other grid cells within the ice grid, the cell is assigned a value greater than 0. Integers 1-10 indicate the number of tenths of 1° latitude square covered by ocean. Values from 11-20 are found near land areas where adjacent grid points lie over land. Again, please refer to the online documentation.
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  3. SMMR
    Online Documentation:
    http://nsidc.org/NSIDC/CATALOG/ENTRIES/nsi-0079.html

    The NSIDC has another relevant ice concentration data set. This data set is called "Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I". SMMR stands for Scanning Multichannel Microwave Radiometer, and DMSP SSM/I is an acronym for the Defense Meteorological Satellite Program's Special Sensor Microwave/Imager.
    Temporal Coverage:
    Monthly gridded sea ice concentrations from October 1978 to December 1999.
    Grid Spacing, Dimensions:
    The data are digitized onto a polar stereographic grid. Each grid cell covers 25 km x 25 km, and the dimensions of the grid are 304x448.
    Grid Coordinates:
    A FORTRAN routine, LOCATE.FOR, was downloaded from the ftp site containing the source data. This routine was used to produce latitude and longitude values from I,J indices. Reference coordinates are available on the online documentation, as well as a diagram of the arctic grid.
    Ice Concentration:
    Each monthly data record has a header, which contains the month and year, followed by the ice concentration data. The concentration values are in integer format, and the concentration values (%) were multiplied by 10 such that the values range from 0 to 1000. No separate land mask is necessary, as a value of -800 indicates land. It is important to note that due to the inclination the satellites' orbits, there is a "hole" above 85° N for the SMMR data, and above 87° N for the SSM/I data. These data values are flagged by a value of -100 in the data sets. All data up to July 1987 (inclusive) have the larger hole extending to 85° N. From August 1987 onwards, the smaller hole came into effect. To be consistent, however, all data above 85° N were treated as land.
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  4. Canadian Global Coupled Model, CGCM1
    Online Documentation:
    http://www.cccma.bc.ec.gc.ca/models/models.html

    CGCM1 data is not observed data, but model output. The model output used for interpolation from the Canadian Center for Climate Modeling and Analysis originated from the first version of the Canadian Global Coupled Model, CGCM1. While this model did not produce ice concentration values, it did produce ice mass (kg/m2) values. Three data sets were available for downloading: a control, ghg, and ghg+1. The different features of these sets are described on the above web site. Note that the CGCM1 data used in this discussion was the GHG+A (greenhouse gas + sulphate aerosol) data set.
    Temporal Coverage:
    Monthly data from 1900 to 2100 were available.
    Grid Spacing, Dimensions:
    The grid spacing is approximately 3.75° x 3.75°. The dimensions of the grid can be specified by the user, before downloading the data. In our case, to choose the northern hemisphere, the dimensions were 96x24.
    Grid Coordinates:
    While the longitudes are evenly spaced by 3.75°, the latitudes are not spaced evenly. The latitude coordinates are available on the CCCMA web site.
    Ice Concentration:
    The ice mass per unit area (M) data were converted into ice concentration data (C) by the following formula, courtesy of Dr. Greg Flato: C=1-(45./M)1.25. The value of 45 kg /m2 is a "cutoff" value that corresponds to a minimum ice thickness of 5 cm, assuming that the density of sea ice is 910 kg/m3. Any grid cell containing less than this cutoff value were assumed to have zero concentration. A separate land mask was downloaded from the CCCMA web site. In this mask, a value of 0. indicates sea, while 1. indicates land.
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  5. Atmosphere Ocean Model, GISS
    Online documentation:
    http://aom.giss.nasa.gov

    The Goddard Institute for Space Studies (GISS) has a recent (1999) Atmosphere-Ocean Model which produced, among dozens of results, both ice concentration data and ice mass per unit area values. Extensive documentation about this model, and its six simulations, are available on the AOM web site, listed above. Note that for this discussion, the data from the C091 simulation (GHG+A) was used.
    Temporal Coverage:
    Monthly data from January 1950 to December 2099.
    Grid Spacing, Dimensions:
    The grid spacing is 5° longitude by 4° latitude. The dimensions are 72x46.
    Grid Coordinates:
    While no separate file containing grid coordinates was available, there was sufficient documentation for the user to calculate grid coordinates.
    Ice Concentration:
    The ice concentration data were represented as percentage values, ranging from 0. to 100. The ice mass per unit area data were also in REAL format. The same conversion calculation used for CCCMA model output was used for the GISS ice mass data.

    A land mask was available on the AOM site, called Z72X46N. A value of 0 indicates land, while 1 indicates ocean.
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  6. Hadley Centre's Second Generation GCM, HadCM2

    The ice concentration and thickness data were obtained from a 240-year integration, with greenhouse-gas and sulphate forcing.

    Online documentation:
    http://www.cru.uea.ac.uk/link/experiments/2_experi_intro.html
    Temporal Coverage:
    Monthly data from September 1860 to August 2100
    Grid Spacing, Dimensions:
    The grid spacing is 2.5° latitude by 3.75° longitude. The dimensions are 96x73.
    Grid Coordinates:
    Latitude and longitude values were made available by the Hadley Centre.
    Ice Concentration:
    Ice concentration data were presented as REAL numbers, ranging from 0. to 1. Ice thickness values were also available as REAL numbers, in units of meters.

    No separate land mask was necessary, as all land values were flagged as -1.
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  7. Atmosphere Ocean Model R15, GFDL
    (Geophysical Fluid Dynamics Laboratory)

    As with CGCM1, several simulations of the R15 coupled ocean-atmosphere model exist. For this discussion, ice thickness data were obtained from the 300-year 'CO2 + SUL' integration, as documented in Haywoodet al., 1997.

    Documentation:
    Haywood, J. M., R. J. Stouffer, R. T. Wetherald, S. Manabe, and V. Ramaswamy. Transient response of a coupled model to estimated changes in greenhouse gas and sulfate concentrations. Geophysical Research Letters, 24(11), pp.1335-1338, 1997.
    Temporal Coverage:
    Monthly data from January 1766 to December 2065
    Grid Spacing, Dimensions:
    The grid spacing is approximately 4.44° latitude by 3.75° longitude. The dimensions are 96 x 40.
    Grid Coordinates:
    A separate file containing grid coordinates was made available by GFDL.
    Ice Concentration:
    Ice thickness per unit area were first converted into ice mass per unit area (M) and then converted into ice concentration data (C) by the following formula, courtesy of Dr. Greg Flato: C=1-(45./M)1.25. A separate land mask was available. A value of 0 indicates land, while a value of 1 is ocean.
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  8. IOS Arctic Ice-Ocean Model
    Documentation:
    This is a 3 dimensional ocean model coupled to a dynamic and thermodynamic model for ice and snow. Because atmospheric and river forcing are assigned from data, this model is not used to forecast future ice conditions. For further information see Nazarenko, L., G. Holloway and N. Tausnev, 1998: Dynamics of transport of 'Atlantic signature' in the Arctic Ocean. J. Geophys. Res., 103, 31003-31015.
    Temporal Coverage:
    Monthly data from January 1948 to December 1999
    Grid Spacing, Dimensions:
    The grid spacing is 0.5° by 0.5°. The dimensions are 91x67.
    Grid Coordinates:
    The FORTRAN routine RDATA.F, as described in the Interpolation section, describes the calculation of the grid coordinates.
    Ice Concentration:
    The ice concentration data are real numbers, ranging from 0. to 1. A land mask, called kmt.arc, was available. A value of 0 indicates land, where all other values greater than 1 indicate ocean.
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