The ice model receives ocean and atmosphere states and fluxes from the coupler and returns aggregate ice states and fluxes. Tables 2 and 3 in the Scientific Documentation list the fields that are exchanged. The flux coupler multiplies the fluxes it receives from the ice model by the ice area, so before fluxes are sent to the coupler, they are divided by the ice area (see module ice_scaling.F). To increase the performance of CCSM2, a packed buffer is exchanged with the coupler that contains a reduced set of information.
How this data is reduced depends on the model configuration. For the fully coupled (B) configuration, information is sent to the coupler only in ocean grid cells that have a non-zero ice area (see module ice_coupling.F). The prescribed ice model, or F configuration, sends data in ocean grid cells where the monthly averaged ice concentration bracketing the current date and the next monthly average are non-zero. For the M configuration, data is sent in ocean grid points for latitudes south of -40 degrees and north of 35 degrees (see module ice_grid.F). The land mask is modified to screen out these points; the area between these latitudes appears as land in the history files.
The coupler returns information to the ice model via a packed vector. Beginning at the equator, the coupler searches for the first grid cell where either the ice concentration is greater then zero, there is potential to form ice, or data was sent by the ice model. An additional five grid points are then added. This is done in both hemispheres.
The packing of the buffer exchanged with the coupler and the multiplication of the fields received from the ice model by the ice area in the coupler affect the information written to the history files. These effects are discussed in the next section.
Before fields are received from the coupler, the corresponding arrays in the ice model are set to zero and only the active cells are filled in. As a result, information sent to the ice model is not known everywhere, but all grid values are written to the history file. See section 18.104.22.168 for information on how fields are averaged before being written to the history file. The affected fields are
These fields can be retrieved from the ocean or atmosphere history files, so they have been removed from the ice history files via the namelist. If performance is not a problem, the buffer can be sent to the coupler unpacked, then all of the above fields are valid.
The coupler multiplies fluxes it receives from the ice model by the ice area. Before sending fluxes to the coupler, they are divided by the ice area in the ice model. These are the fluxes that are written to the history files, they are not what affects the ice, ocean or atmosphere, nor are they useful for calculating budgets. The division by the ice area also creates large values of the fluxes at the ice edge. The affected fields are:
When applicable, two of the above fields will be written to the history file: the value of the field that is sent to the coupler (divided by ice area) and a value of the flux that has been multiplied by ice area (what affects the ice). Fluxes multiplied by ice area will have the suffix _aice appended to the variable names in the history files. Fluxes sent to the coupler will have "sent to coupler" appended to the long_name. Fields of rainfall and snowfall multiplied by ice area are written to the history file, since the values are valid everywhere and represent the precipitation rate on the ice cover.