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

[Nadav Mantel]

Hey everyone!

Thank you so much for replying to my questions, very helpful and really
appreciated!
I think these answers will be extremely valuable when considering different
frameworks for me in the future.

Have a great weekend and once again thanks for all your help!
Nadav

On Fri, Aug 26, 2022, 6:41 PM Menemenlis, Dimitris (US 329B) <
dimitris.menemenlis at jpl.nasa.gov> wrote:

> Hi Nadav, I just discussed answers to your questions with group in cc.
>
> 1. We used MITgcm in hydrostatic configuration.
>
> 2. We used KPP because it was the parameterization used in the global
> model that provided the boundary conditions, so mostly for inertia reasons
> and due to lack of bandwidth to explore all possible options.  But you are
> right in pointing out that background diffusivity and viscosity in KPP is
> meant, in part, to represent internal wave breaking.  Note that below the
> surface boundary layer, KPP includes a Richardson-number based
> representation of mixing.  This is why it makes sense to turn off the
> background diffusivity and viscosity terms when you are starting to
> explicitly resolve internal waves in the simulation.
>
> 3. Breaking of IWs in our simulations is parameterized by the KPP
> Richardson-number based term, since our resolution is insufficient to
> resolve actual breaking.  With the exception of the southwest corner of our
> domain, IWs do not have much opportunity to shoal in our open-ocean
> regional simulations.  I think this is a big difference with your domain,
> where much of the vertical mixing physics in your specific case may be
> driven by interactions with bottom bathymetry.
>
> 4. For realistic representation of vertical shear, more vertical levels is
> definitely better.  If you can afford to increase vertical levels, you
> definitely should, and compare with the coarser-vertical-resolution
> simulations to establish impact of vertical resolution on the solution.
>
> Cheers,
>
> Dimitris Menemenlis
>
>
> On Aug 26, 2022, at 5:11 AM, Nadav Mantel <nadav.mantel at mail.huji.ac.il>
> wrote:
>
> Hi Dimitris,
>
> Thank you for responding to my email.
> I have a few questions regarding the paper and the study.
> 1. In the study did you run a non-hydrostatic or hydrostatic model?
> 2. Why in the first place use KPP in IW parameterizations? Obviously it is
> an extremely well known and widely used vertical parameterization package
> but isn't meant to include IW in the first place. What was the motivation
> not to research KL10, or one of the richardson packages (PP81, MY82, GGL90)
> which were designed for this reason?
> 3. If I understood correctly, in the study you researched IW presence, its
> shear and other physical aspects of the IW spectrum, yet you didn't look at
> the shoaling and breaking of said IWs, once again, if I understood
> correctly because I might be missing some crucial point. Would the findings
> of the study (remove KPP background parameters) also hold for this type of
> parameterization?
> 4. In the study you use high vertical resolutions. I have "inherited" a
> model which uses 32 layers, in an elongated and rather deep basin. In your
> opinion, should I increase vertical layers or do the MITgcm packages
> overcome the reduced resolutions?
>
> Thanks so much for your input and for sharing the paper,
> Nadav
>
> On Thu, Aug 25, 2022 at 11:15 PM Menemenlis, Dimitris (US 329B) <
> dimitris.menemenlis at jpl.nasa.gov> wrote:
>
>> Hi Navad, here is a recently-published paper that may be relevant to some
>> of the questions that you ask:
>> https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL099614
>>
>> But note that the above study pertains to the representation of internal
>> waves in an open ocean region, as opposed to a narrow, elongated gulf.
>>
>> Dimitris Menemenlis
>>
>> 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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