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

[Jeffery R Scott]

Thanks for the comments everyone.

I’ll see what I can add to that section of the manual that Baylor originally wrote, to help clarify, and would encourage others to look as well.
Feel free to either update the doc and do a PR, or email me any info you think would be helpful to include.

-Jeff



On Apr 16, 2018, at 9:27 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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