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Adding a detailed description of the DINO configuration: Summary of bathymetry, forcings, default namelist, etc.

The solar forcing was taken from the Gyre configuration. There, the domain extends from 15°N to 50°N such that the solar forcing results in a downward heatflux everywhere. In DINO this results in a negative heatflux north of ~60°N: See Caneill.

Suggestion: Remove solar radiation, but include its effects in the temperature restoring T*.

While

xgcm.grid.average(EmP, ['X', 'Y']) ~ 1e-21

but

xgcm.grid.integrate(EmP, ['X', 'Y']) ~ 1

because of the very large extend of the domain. This leads to ~ 3g/s mass-flux.

--> 1e8 kg in 1000 years

If the subdomain of mpi is smaller than the sill, the eastern boundary of that subdomain. This issue first appeared in nemo_4.2.1, but might be coincidence.

If the domain_cfg_out and mesh_mask are generated on one processor (or few) and read from file (issue #17 ) this issue is patched.

Starting the same experiment with a different value for rn_e1_deg changes the total volume of the domain:

• for rn_e1_deg = 1. --> V = 2.70686566e+15
• for rn_e1_deg = 0.25 --> V = 2.77492743e+15

This (at least most of the difference) comes from the fact that the volume of the total domain stays (nearly) the same, but the masked boundary is wider the coarser the grid. Thus the ration land/ocean decreases with horizontal resolution.

Ideas to solve:

1. Mask more land points when going to higher resolution.
   --> At e.g. 1/32° resolution this would mean 31 additional rows at each boundaries
   --> Could use NEMO functionality to exclude processes with only land?
2. Define the horizontal grid through L_y, L_x, rn_e1_deg
   --> the periodic row in the channel would not conserve it's Volume under change of resolution
   --> If neglecting the last row in all diagnostics, does this lead to issues?

If doing a true conservative interpolation of the inner points (also conserving volume) and carefully compute first and last row in i-direction? Or conservative interpolation from LR --> HR with small error already sufficient? (slight heating of the domain with higher resolution...)

--> Option 2

Backed up by Wolfe & Cessi (2011) and crude estimates from the IPSL climate model, the SST should always be warmer in the northern hemisphere.

Needed for experiments vopikamm/dino-experiments#1 . When choosing a less steep Scottia-arc, differences between the western and eastern channel bathymetry become bigger, violating a smooth periodicity.

Idea: Use the central gauss-ring profile (western boundary) to taper the entire channel --> periodic bathymetry

Currently NEMO does not accept analytical forcings from usrdef_sbc.F90 AND forcing fields read in fldread.F90. The idea is to have the functionality of fldread.F90 implemented in the usrdef_sbc.F90.

All usrdef files need some cleaning up with old and unused functions.

This doesn't seem to affect the results since it is only used for the surface momentum stress, which looks fine:

Need to implement Zanna & Bolton in NEMO.

Right now, with every restart, the domain_cfg is rebuild from scratch (~ 8GB of data being computed)

As a result from the experiment in vopikamm/dino-experiments/issues/4 : surface freshwater flux in the form of a SSS-restoring does not allow for a sufficient meridional density gradient and outcropping isopycnals in the channel. Go to a E-P fresh-water flux as in Wolfe & Cessi 2014. But adapt to values from IPSL climate model E-P output.

Diagnosing the monthly MLD of a DINO test-run suggests a bug in the forcing. The MLD appears to have an semi-annual cycle, e.g. January = July.

Right now spin-up takes forever, because all deepwater needs to be formed. Create an initial case which accounts for this.

Romain already has implementation init_case=4, but needs to be tested:

--> start short experiment with init_case=4 and check densest water ~ 1027

From meeting with Feiyu Lu. Having temperature restoring to zonal profile will decrease variability at the surface for high resolution runs (But should reflect a coupling to the atmosphere sst).
Downside: qns does not represent lwr, latent, sensible heatflux depending on the sst fields, but is simply imposed (check with Julie how this is done in climate models)

The retroaction term T* from Romain (low meridional gradient at boundary) demands for negative meridional S* gradients to have a meridional surface density gradient supporting the ACC. Choosing T* from Munday with seasonal cycle and S* with adapted and asymmetric boundary values. Choose salt minimum on the equator.