For which variables is the tripolar grid an issue that needs to be considered when performing analyses?  

South of 65N, the horizontal grid used by the CM2.X ocean and sea ice models is a regular rectangular grid and therefore it should pose no problem for analysis programs when the Arctic is not being considered. The non-regular nature of the tripolar grid only occurs at locations north of 65N, and only applies to the ocean and sea ice model components, not the atmosphere or land surface.

Many analyses will not be at all affected by the tripolar grid (e.g., analyses of the tropical oceans, or the Southern Hemisphere). Only analyses that include the Arctic (including global analyses) will need to account for the tripolar grid.

Users can follow one of two general approaches when dealing with the tripolar portion of the grid.

1. Though we at GFDL have not developed a single interpolation method that yields results that are suitable for all common analysis applications, individual researchers may determine that a certain interpolation method of their choosing is appropriate for their particular analyses. In such cases, they can download the tripolar data files and perform the desired interpolation themselves.
2. One may use the model output are it is archived on the model's native grid in order to facilitate quantitatively accurate results. Additional grid variables and metadata have been provided to aid in performing quantitatively accurate analyses. This is the most common approach being used at GFDL. See the CM2.X model ocean and sea ice grids information page for more specific information.

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