[MITgcm-support] Regional high-res model configuration

[Martin Losch]

Hi Stanislav,

generally your parameters look good, so comments below

> On 21. Apr 2020, at 11:23, Stanislav Martyanov <martyanov.sd at gmail.com> wrote:
> 
> Hello, dear colleagues!
> 
> I am configuring the MITgcm for the Kara Sea region. With the curvilinear grid, the model's resolution is: dx=500-1200 m, dz=2 m in upper layers, and up to 20 m in the deepest. The minimum model depth is set equal to 5 m. I use the pure r vertical coordinate (not r*) for now. Because of the curvilinear grid, I use vectorinvariant package. Other packages used are: seaice, my82, exf, cal, obcs.
> 
> Having carefully read (once again) the newest version of the online-manual and browsed the code, I have configured almost all necessary model parameters, but still some questions remain. They are qiute specialized, so I could not find the needed information in puplished papers. But for those experienced with MITgcm, they might be easy to answer. I will appreciate any advise!
> 
> 1) The newly added feature with partial cells (#undef EXCLUDE_PCELL_MIX_CODE in CPP_OPTIONS). The parameter pCellMix_select = 0 by default, which means that the enhanced mixing is OFF in bottom and surface layers. The parameters intended for the enhanced mixing in the inner layers are also OFF by default: interViscAr_pCell and interDiffKr_pCell = FALSE. Are this option and the corresponding run-time parameters really important for such configuration (Kara Sea)? Any experience with them?
I have no experience with this, but I think you can safely keep this turned off.
> 
> 2) I use the following viscocity and diffusivity values, intending to use the Smagorinsky viscocity for lateral turbulent exchange:
>  viscAh = 1.0,
I would use viscAhGrid or viscAhGridMin for this (something small)
this is only 2D Smagorinsky. I would use 2D Leith instead.
>  viscC2smag = 3.0,
setting viscAhGridMax (something a little smaller than 1) may be necessary
>  viscAr = 1.0e-5,
depending on your advection scheme, horizontal diffusivities can be zero (I would use 77, 33 or 7 for advection)
>  diffKhT = 1.0,
>  diffKhS= 1.0,
>  diffKrT = 1.0e-5,
>  diffKrS = 1.0e-5,
> But for diffusivity there is no Smagorinsky analogue. What approach can be the most suitable in this case?
> 
> 3) In the paper "ECCO version 4 - an integrated framework... " by Forget et al., 2015, the authors decided to switch OFF the C-D sheme and to switch ON the Implicit vertical advection option. But they investigated the global scales, not high-res. From your experience, can their advise be applyed to the high-res ocean simulations?
Don’t use the CD scheme, if necessary use small biharmonic viscosity instead. Implicit vertical advection is probably not required either
> 
> 4) The MY82 package does not allow using the convective adjustment (cAdjFreq) and ivdc_kappa. Does it mean that the MY in MITgcm works fine with vertical instability cases? Actually, it should, as follows from J. Mellor's papers, but this question arose when I was investigating the GGL90 code, where I found the line "convective adjustment might be needed even with ggl90"…
Why do you want to use the MY82 package? I’d prefer GGL90 or KPP (although at your resolution, KPP might be noisy (see this thread <http://mailman.mitgcm.org/pipermail/mitgcm-support/2020-April/012427.html>).
You can just comment out the stop-statement in the code and use MY82 with other convective adjustment, but it should (like GGL90) remove the instabilities, because it’s also Richardson number based. MY82 is not really used that much (at all?).

Martin
> 
> Once again, I will appreciate any advise!
> 
> PS: Sorry for large wall-of-text here, but I tried to be concrete. :-)
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