6.2.3. Sea-ice schemes

From Version 8, Surfex handles sea-ice either :

• by using sea-ice cover forcing data from PREP file
• or by activating a sea-ice prognostic scheme.

This allows to compute surface fluxes which are much more realistic than when using only Sea Surface Temperature (SST). A report on this development is available in V8 documentation

A sea-ice scheme is activated at the PREP stage using parameter CSEAICE_SCHEME of NAM_PREP_SEAFLUX (see 5.3.1. Namelist NAM_PREP_SEAFLUX). It also involves some settings in the relevant namelist : 6.2.5. Namelist NAM_SEAICEn. A sea-ice scheme must be provided with Sea Surface Temperature (SST), and Salinity (SSS) fields, in a way described at 6.2.1. Namelist NAM_SEAFLUXn

When a sea-ice scheme is not activated, sea-ice cover is anyway handled if CINTERPOL_SIC /= NONE in NAM_SEAICE , then :

• sea-ice cover forcing data must be provided in the PREP file
• sea surface temperature is used as sea-ice temperature on locations where sea-ice cover is not zero
• a constant sea-ice albedo is used (see XCST_ICE_ALB in 6.2.5. Namelist NAM_SEAICEn)

In both cases :

• there are two options for turbulent exchange coefficient calculation over sea-ice (see XCD_ICE_CST in 6.2.5. Namelist NAM_SEAICEn).
• sea-ice concentration becomes a prognostic field (named SIC)
• all usual SEA scheme diagnostics (as e.g. LE_SEA, LEI_SEA, CD_SEA, SWU_SEA, FMV_SEA, Z0_SEA, see 9.2.2. For each tile and all tiles aggregated) then represent the linear weigthing of open sea and sea-ice values (weighted by sea-ice cover)
• the same diagnostics are provided for sea-ice only (e.g. LE_SEAICE) See 9.2.2. For each tile and all tiles aggregated.

The Gelato sea-ice prognostic scheme is the only sea-ice scheme yet managed with NAM_SEAICE. It is described at 6.2.4. Gelato sea-ice scheme