[MITgcm-support] Choosing Leith biharmonic co-efficient?

[David Ferreira]

Hi all,
May be useful to mention that Fox-Kemper et al. have also developed a QG Leith scheme, same idea as 2D Leith but viscosity is proportional the QG PV gradient, instead of just the vorticity gradient (one may or may not add the divergent part to this).
The claim is that it is slightly more general than the "normal" 2D Leith scheme


Bachman, S. D., Fox-Kemper, B., Pearson, B., 2017. A scale-aware subgrid model for quasi-geostrophic turbulence. J. Geophys. Res. 122 (2), 1529– 1554.

There is another paper in Ocean Modelling.

cheers,
david


________________________________
From: MITgcm-support [mitgcm-support-bounces at mitgcm.org] on behalf of Jody Klymak [jklymak at uvic.ca]
Sent: Monday, April 16, 2018 10:17 AM
To: mitgcm-support at mitgcm.org
Subject: Re: [MITgcm-support] Choosing Leith biharmonic co-efficient?

Hi all,

Thanks so much for your advice and in particular the Fox-Kemper and Menemenlis reference (which Dmitris had given me in another context, so I guess I should have read it ;-).

Having quickly read it (on a plane, at 5:30 AM), I’m a little unsure about the applicability of Leith once horizontal scales get down to a km or so, particularly if one wants to have a reasonable internal wave field, there is the statement that the divergence-sensing term will negatively impact “high-frequency” internal waves.

I will be playing with this the next couple of months, but wanted to know the community insights into these parameterizations.  Certainly the 10-km spinup expt I’m doing now needed Leith biharmonic viscosities to make a nice flow.

Thanks again,   Jody



On Apr 16, 2018, at  6:27 AM, Ryan Abernathey <ryan.abernathey at gmail.com<mailto:ryan.abernathey at gmail.com>> wrote:

Jody,

I assume you are talking about the config you got from Dhruv. The values we use in those runs were taken from Dimitris Menemenlis and Chris Hill's LLC simulations. The exact same settings are used for 1/12, 1/24, and 1/48 degree global simulations. (Although I do recall that Dhruv had to make some changes related to boundary conditions.)

-Ryan

On Mon, Apr 16, 2018 at 8:59 AM, Malte Jansen <mfj at uchicago.edu<mailto:mfj at uchicago.edu>> wrote:
Just to add on to this: the Leith viscosity is supposed to be "scale aware" (at least within a QG turbulence regime), such that the non-dimensional coefficient should be independent of the grid-scale.

-Malte



On 4/16/18 3:16 AM, Martin Losch wrote:
Hi Jody,

my reference is pkg/mom_common/mom_calc_visc.F where you can find this:

C     RECOMMENDED VALUES
C     viscC2Leith=1-3
C     viscC2LeithD=1-3
C     viscC4Leith=1-3
C     viscC4LeithD=1.5-3
C     viscC2smag=2.2-4 (Griffies and Hallberg,2000)
C               0.2-0.9 (Smagorinsky,1993)
C     viscC4smag=2.2-4 (Griffies and Hallberg,2000)

And I think this is where it is described:
B. Fox-Kemper and D. Menemenlis. Can large eddy simulation techniques improve mesoscale-rich ocean models? In M. Hecht and H. Hasumi, editors, Ocean Modeling in an Eddying Regime, volume 177, pages 319-338. AGU Geophysical Monograph Series, 2008.
http://www.geo.brown.edu/research/Fox-Kemper/pubs/pdfs/FoxKemperMenemenlis08.pdf

Martin

On 14. Apr 2018, at 22:42, Jody Klymak <jklymak at uvic.ca<mailto:jklymak at uvic.ca>> wrote:


Hi all,

Is there a good reference and/or ruls of thumb for choosing the Leith biharmonic co-efficient? i.e. `viscC4Leith` and `viscC4Leithd`, with particular interest in how the size of the grid affects the choice?  I’m using someone else’s setup, using Leith works great for making the flow look reasonable, but it would be nice if it was turned down as much as possible, particularly when I downscale to a smaller grid size…

Thanks a lot,   Jody
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--
Malte F Jansen
Assistant Professor
Department of the Geophysical Sciences
The University of Chicago
5734 South Ellis Avenue
Chicago, IL 60637 USA


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