Forcing values are updated based on the value of *_interp_inc and whether the value of the forcing term depends explicitly on the ocean state, as detailed below.
Wind stress (ws) and atmospheric pressure (ap)
forcing currently do not depend explicitly on the ocean state so
the forcing terms in the equations are updated depending on the
value of [ws,ap]_interp_freq. For example, with
ws_data_type = 'monthly-calendar',
ws_interp_type = 'linear', and
ws_interp_freq = 24., the code will linearly interpolate monthly wind stress values at the beginning of each day and will use this interpolated value for one model day.
Potential temperature and salinity forcing typically do explicitly depend on the ocean state (for example, restoring to climatology depends on the difference between the climatological value and the current model value) so the forcing terms in the equations are evaluated every timestep. However, just like with the wind stress and atmospheric pressure, the value of the data used in calculating the forcing terms depends on the value of *_interp_freq. For example, with pt_interior_data_type = 'monthly-calendar', pt_interior_interp_type = 'linear', pt_interior_interp_freq = 48., and pt_interior_formulation = 'restoring', the code will linearly interpolate monthly potential temperature values at the beginning of each 2-day interval and will use this interpolated value for two model days when calculating the forcing. Again, the actual forcing term is evaluated every timestep, but the value that is being restored to stays constant over the 2 day period.