[MITgcm-support] Regional high-res model configuration

Tue Apr 21 13:15:44 EDT 2020

Hi Martin!

Thanks for your reply!

Right to the business:

>>I would use viscAhGrid or viscAhGridMin for this (something small)
To be honest, I hardly understand the nature of viscAhGrid parameter...
While viscAh can be seen as some kind of  constant physical background
viscosity not resolved by the main horizontal turbulence parameterization
used (Smagorinsky, Leith, etc),  viscAhGrid seems like some numerical
trick. From its formula in MOM_CALC_VISC it can be concluded that it has
something to do with grid size (just like Smagorinsky).

>>this is only 2D Smagorinsky. I would use 2D Leith instead.
The only reason I chose Smagorinsky parameterization was its dependence on
grid resolution and dynamical regime (velocity gradients are involved). But
your alternative (viscAhGrid +  viscC2leith), perhaps, does the same in a
combined manner.

>> setting viscAhGridMax (something a little smaller than 1)
>> may be necessary
In MOM_CALC_VISC  the recommended value for viscAhGridMax is 1. What value
would you use?

>> depending on your advection scheme, horizontal diffusivities
>> can be zero (I would use 77, 33 or 7 for advection)
I use the advection scheme 33 (3-order DST with Sweby flux limiter) for T,
S and seaice.

Does the next set of parameters seem better than the previous one?
viscAhGrid = 0.5, viscAhgridmax = 1.0, useFullLeith = .TRUE., viscC2leith =
1.0, viscC2LeithD = 1.0, viscAr = 1.0e-5.
Diffusivities: diffKhT = 1.0, diffKhS= 1.0, diffKrT = 1.0e-5, diffKrS =
1.0e-5.
Here I additionally set viscC2LeithD as it is recommented in the manual (a
damping specifically targeting purely divergent instabilities near the
gridscale).

>> Don’t use the CD scheme, if necessary use small biharmonic viscosity
>> instead. Implicit vertical advection is probably not required either
OK, the CD_scheme is omitted then, thank you! But can Implicit vertical
advection significally alter the results? I just hoped to use it in order
to somewhat increase the time step.

>> Why do you want to use the MY82 package?
The only reason is that I previously used it and familiar with it.
Moreover, the MY is a well-known mixing scheme, and both its good and bad
sides are also documented.

>> 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>).
Previously our team used the KPP for another configuration, but for now I
decided to omit it. I read the thread you mentioned, and it was the last
straw to find another scheme :-)

As for GGL90, I did not previously used it at all. From the original paper
by Gaspar et al, 1990, I know that it has only one prognostic equation (for
TKE) and that the turbulent length scale is diagnosed rather than
prognosed. From your experience, can you  recommend it over the MY82?

 >> but it should (like GGL90) remove the instabilities,
>> because it’s also Richardson number based
Yes, I know, and that is why I was surprized by the comment in the code
"convective adjustment might be needed even with ggl90". Do you use GGL90
with or without convAdj or  ivdc_kappa?

I also know that you are the author of the SEAICE package for MITgcm, so
could you tell, is it OK for now to use the newly added feature
SEAICE_ALLOW_MOM_ADVECTION
and corresponding run-time parameters SEAICEmomAdvection=TRUE,
SEAICEuseMetricTerms
= TRUE, and SEAICEuseFluxForm=TRUE if my configuration uses curvilinear
grid (and that's why I must use vectorInvariant for momentum)? The
vectorInvariant
does not use the metric terms for momentum, should I use them for SEAICE on
my grid? And as I understood, there is no alternative for
SEAICEuseFluxForm?

Stanislav

вт, 21 апр. 2020 г. в 14:31, Martin Losch <Martin.Losch at awi.de>:

> 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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>
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