This issue should be the main issue describing what is needed to couple neXtSIM to NEMO via OASIS. It may refer to other issues as they arise to allow us to focus on those.

Exchange fields required for the coupling

ice -> ocean

• ice-ocean stress in x-direction [Pa]
• ice-ocean stress in y-direction [Pa]
• ice-ocean stress magnitude [Pa]
• evaporation minus precipitation [kg/m^2/s]
• non-solar heat fluxes (longwave + latent + sensible) [W/m^2]
• short-wave flux [W/m^2]
• surface salt flux [kg/m^2/s]
• surface fresh-water flux [kg/m^/s]
• sea-ice concentration [0-1]

ocean -> ice

• ocean velocity in x-direction [m/s]
• ocean velocity in y-direction [m/s]
• sea-surface height [m]
• sea-surface temperature [°C]
• sea-surface salinity [PSU]
• height of first ocean layer [m]
• the fraction of short-wave radiation penetrating the first ocean layer [0-1]

Location of values on the (Arakawa) grid and vector rotation.

All values are passed at the centre of the cell (T-point), with the following exceptions:

• NEMO sends ocean velocities located at the U-point for x-direction and V-point for y-direction values.
• NEMO expects ice-ocean stresses located at the U-point for x-direction and V-point for y-direction values.

The two models have different definitions of x and y directions, so these vectors must be rotated before or after coupling. The most practical way to handle this is to interpolate both components to the centre (T) point, do the rotation there, and interpolate back to U/V points if needed. We may think of a more sophisticated way to handle this.

Tasks to complete the coupling

• Make sure neXtSIM calculates all the fields needed by NEMO
• Make sure neXtSIM can use all the fields provided by NEMO
• For fields calculated by neXtSIM, make sure we can pass the fields from the physics routine that generates them to the coupler interface
• For fields provided by NEMO, make sure we can pass the fields from the coupler interface to the physics routine that needs them
• Initiate the state of OASIS at the start of the run and close everything at the end
• Implement an OASIS "send" interface in neXtSIM
• Implement an OASIS "receive" interface in neXtSIM

See also issues #69 and #80