Sea surface salinity restoring

[aekiss]

We have sea surface salinity restoring in ACCESS-OM2 - see sec 3.5.2 of the tech report. I assume we'll need this in ACCESS-OM3, so we should work out how to do it in MOM6.

[ezhilsabareesh8]

In MOM6, salinity restoring is done by setting RESTORE_SALINITY = True in MOM_input file. Unlike MOM5, which relies on the restoring time scale (salt_restore_tscale) (In OM2 tech report), MOM6 employs a more physically relevant approach by utilizing the piston velocity which is a ratio of surface vertical grid spacing to restoring time scale, represented as FLUX_CONST. The piston velocity is set to 0.11 m/day (see this commit Added salinity restoring), similar to OM2.

To apply salinity restoring as a salt flux, SRESTORE_AS_FLUX = True can be set, and by default, salt is restored under sea-ice in MOM6 based on the criteria SST <= Tf (refer here). To limit the sea surface salinity mismatch, the MAX_DELTA_SRESTORE parameter can be specified, similar to OM2, a restore limit of 0.5 PSU is added here.

MOM5 has a spatially constant offset to ensure a net zero salt restoring flux for each timestep (zero_net_salt_restore = true), no specific flag has been found in MOM6 for this purpose. I presume that the net salt restoring flux is set to zero by default in MOM6.

[adele-morrison]

There is an option for zeroing the net restoring in MOM6:
ADJUST_NET_SRESTORE_TO_ZERO = TRUE

There's also an additional option that wasn't available in MOM5 that would be interesting to try:
ADJUST_NET_SRESTORE_BY_SCALING = False (If true, adjustments to salt restoring to achieve zero net are made by scaling values without moving the zero contour.)

[ezhilsabareesh8]

Thanks for the information @adele157. I have incorporated the changes in the MOM input (commit), ADJUST_NET_SRESTORE_TO_ZERO is set to True, enabling the zeroing of the net restoring in MOM6. Additionally, I have also included ADJUST_NET_SRESTORE_BY_SCALING = False in the MOM input.

[dougiesquire]

Apologies, I missed this discussion and also added salt restoring in ACCESS-NRI/access-om3-configs#5

[micaeljtoliveira]

Done in ACCESS-NRI/access-om3-configs#5