The thermodynamic calculations involve one grid point at a time (see module ) so that a purely thermodynamic model integration is bit-for-bit independent of the domain decompostion (i.e. the exact values of ), while the dynamic calculation depends bit-for-bit upon domain boundary conditions, and therefore on the exact values of and . The sea ice model climate is not sensitive to the precise domain decomposition.
The actual source code uses and for and respectively, referring to the number of processors in the x direction and in the y direction (these parameters are set by a pre-compiler; see the CSIM User's Guide Version 4). The module defines the local subdomain dimensions and their beginning/ending indices. Module computes and assigns the subdomain processor numbers. The module assigns the global domain values.
The module handles the 'unpacking' and 'packing' of the data horizontally after and before exchange with the coupler. This involves excluding latitude bands around the equator that have no sea ice present. Information on the number of latitude bands of data for each hemisphere (i.e. the number of latitude bands of actual hemispheric sea ice but with sufficient equatorwards bands to allow for ice formation along ice edge as well) is included in the data exchange header. As the areas where new ice formation will occur are known to the coupler (based on the freeze/melt potential received from the ocean model), the coupler is able to determine the precise latitude limits. Regions with no ice in the unpacked fields are simply filled with zeros after being received from the coupler.