Caveats Regarding Averaged Fields

In computing the monthly averages for output to the history files, most arrays are zeroed out before being filled with data. These zeros are included in the monthly averages where there is no ice. For some fileds, this is not a problem, for example, ice thickness and ice area. For other fields, this will result in values that are not representative of the field when ice is present. Some of the fields affected are:

• Flat, Fsens - latent and sensible heat fluxes
• evap - evaporative water flux
• Fhnet - ice/ocn net heat flux
• Fswabs - snow/ice/ocn absorbed solar flux
• strairx, strairy - zonal and meridional atm/ice stress
• strcorx, strcory - zonal and meridional coriolis stress

For some fields, a non-zero value is set where there is no ice. For example, Tsfc has the freezing point averaged in, and Flwout has σT_f⁴ averaged in. At lower latitudes, these values can be erroneous.

To aid in the interpretation of the fields, a field called ice_present is written to the history file. It contains information on the fraction of the time-averaging interval when any ice was present in the grid cell during the time-averaging interval in the history file. This will give an idea of how many zeros were included in the average.

The second caveat results from the coupler multiplying 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:

• Flat, Fsens - latent and sensible heat fluxes
• Flwout - outgoing longwave
• evap - evaporative water flux
• Fresh - ice/ocn fresh water flux
• Fhnet - ice/ocn net heat flux
• Fswabs - snow/ice/ocn absorbed solar flux

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.