a. Choose your grid size:
Deep time paleo modelers typically use the low resolution version of CCSM3 (T31_gx3v5; T31 is the land/atmosphere grid, and gx3v5 is ocean/ice grid). We recommend that you choose a CCSM3-supported grid size for your simulation. The most common supported ocean grid sizes are styled after gx3v5 (100 longitudes and 116 latitudes) and gx1v3 (320 longitudes and 384 latitudes). (See the CCSM3 documentation for further details). Although building a new ocean grid with a non-supported grid size is possible, additional changes would need to be made in the ocean and ice source code (Section 18.104.22.168). Examples and tools described in this document are designed for supported ocean grid sizes.
b. Grid pole placement:
The ocean model requires that grid poles be placed over land. Numerically no computation can be done at the convergence point of all longitudes at the grid pole. The ocean model solves this problem by shifting the grid pole away from the geographic pole and placing it over a land mass. (Atmospheric models solve this problem by using numerical filters). Therefore, in CCSM3, if there is no land at the geographic pole, the numerical pole must be shifted over land elsewhere. As long as land exists poleward of ~65o, our tools should be able to create an ocean grid for POP without code modification. However, if no land exists in polar regions, feel free to contact the deep time paleo liaison for consultation. Grid creation may be possible but will require extra effort.
Pole placement is a subjective process, however, we offer a few helpful tips.
- Try to place the grid pole as close to the geographic pole as possible.
- Try to place the grid pole close to the continental edge without creating spurious land cells around the pole disc.
- Try to place the pole 1-2 land cells from the edge of the continent.