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CM2.X model ocean and sea ice grids information
CM2.X model ocean and sea ice grids information.
Analyzing model output on the tripolar grid
To help users make full use of the tripolar ocean and sea ice variables stored on the GFDL Data Portal, we have included additional grid metadata in the table O1c and O1e netCDF files themselves.
We also provide grid information in a separate grid_spec_cm2_ocean_tripolar.nc netCDF file, a copy of which is accessible from all the ocean_tripolar/static/ and ice_tripolar/static/ directories on this server (one file is valid for all CM2.x experiments).
Documentation describing the grid and the supplementary grid information can be found on the Ocean Grid Convention for CM2.0 and CM2.1 web page. Some examples are included to show how to obtain quantitatively accurate area and volume weighting.
We also offer an FAQ entitled How can I visualize the GFDL CM2.x ocean and sea ice models' tripolar grids using the Ferret analysis package? that contains several examples.
It should be noted that model output stored on the tripolar grid has not been subjected to interpolation, and thus does not suffer from any interpolation errors. Having the model output grid be the same as the computational grid used when the model is running results in the the grid cells of the ocean and sea ice tripolar output files being either entirely ocean or entirely land. One does not have to worry about dealing with grid cells that represent partial fractions of land and ocean when working with output stored on the tripolar grid. The trade off is that the non-rectangular tripolar grid is not easily ingested by many analysis software packages (the evolving CF metadata convention should help to address this in the future). Computing quantities such as zonal means can also be challenging.
Since to be accepted at the IPCC WG1 data archive, it is required for model output files to employ a regular rectangular grid, CM2.X ocean and sea ice models output on the tripolar grid can only be found on this GFDL Data Portal, and not at PCMDI.
(NOTE: South of 65N the ocean and sea ice models' native grid follows a rectangular latitude by longitude arrangement that can be easily ingested by most analysis software. Thus, the grids and data values found in the tripolar and interpolated grid files are identical south of 65N.)
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