[MITgcm-support] Help with internal wave breaking and shoaling parameterization package

[Jody Klymak]

Hi Nadav Mantel

Sorry for the apparent bug in KL10 (tracked https://github.com/MITgcm/MITgcm/issues/647 <https://github.com/MITgcm/MITgcm/issues/647>) - there is no fundamental reason it should not work for non-linear equations of state, but apparently has a bug in how density is determined that matters for non-linear equation of state.  Should be straightforward to fix, though I’m 

On the other hand, the mixing parameterizations can pretty easily produce large co-efficients if there are unstable regions.  If you are getting these when you don’t expect them, you should check your forcing.  Maybe do a short run with constant viscosity.  You can also limit the largest viscosity in most of them.  

Cheers,   Jody




> On Aug 25, 2022, at 2:49 AM, Nadav Mantel <nadav.mantel at mail.huji.ac.il> wrote:
> 
> Hey everyone,
> 
> This is a topic that comes up every now and then but I would still really appreciate someone's help.
> I am running a non-hydrostatic regional model for the Gulf of Aqaba\Eilat, an elongated semi-enclosed basin [~200 km long, ~30 km wide ~1000 m deep] with an entry through a shallow sill in the south. The model runs with a horizontal resolution of 300 m and 32 vertical layers with the  differences in depth of 5,10, 12.5, 15, 17.5, ... m and a time step of 10s. I'm forcing tides through the southern boundary using the obcs package. The barotropic flow crossing the Straits of Tiran (our shallow sill) creates large amplitude (50 m in observations) internal waves along the gulf.
> 
> We would like to parameterize the shoaling and general breaking of the internal waves using one of the many packages MITgcm has to offer but we have had some troubles.
> 
> We first intended to use the KL10 package, yet we had uncharacteristic seasonal mixing and when checking the viscosity output we had weird results where in some places we got viscosity coefficients of 3 [m^2/s] whereas the rest of the gulf is much smaller. It could be possibly due to non-linear EOS, I saw in the mitgcm bug tracker that there are issues with anything but linear EOS use in the package.
> 
> We moved on to the richardson number packages, starting with pp81 as it is the simplest. Our problem was that we consistently got the maximum viscosity (a default of 1) in almost all of the second layer, creating once more uncharacteristic mixing with very large diffusivities (60 m^2/s).
> 
> We thought about using KPP as it was the package used in simulating the gulf up until now, but it wasn't designed for this purpose and we are skeptical it would produce good results. 
> 
> Kind of at a loss at this point, and it would be really amazing to get someone's feedback via zoom call on their experiences with internal wave parameterization using any package for regional models.
> 
> Thanks,
> Nadav Mantel
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