[MITgcm-support] A question about the Smagorisnky Coefficient

[Mehmet Ilicak]

Hi all,

I have a question about how to select the smagorinsky coefficient (Cs) 
in MITgcm.
 From engineering turbulence, I know that Cs should be around 0.17*.
If you define the eddy viscosity as

\nu_t=(Cs L2)*|S|

where L is the length scale which generally is the grid size (dx) and S 
is the shear.

Now, I looked at the "mom_common/mom_calc_visc.F" subroutine and I 
realized that the coefficient (viscC2smag) that
I'm prescribing in the data file is divided by pi. Here is the line in 
the code;

IF (calcSmag) THEN
        smag2fac=(viscC2smag/pi)**2
        smag4fac=0.125 _d 0*(viscC4smag/pi)**2
ELSE
        smag2fac=0. _d 0
        smag4fac=0. _d 0
ENDIF

Later, I've read the Fox-Kemper paper** and in there they define the 
eddy viscosity as

\nu_t=(\gammaL2/pi)|S|

I just want to be sure that, if I want to use classical constant 
Smagorinsky coefficient (~0.17),
does it mean that I need to define viscC2smag=0.17*pi=0.5341.
Is this correct, and sorry for inconvenience.

Best,
Mehmet


*Pope, S. B., "Turbulent Flows", 2000.
** Fox-Kemper and Menemenlis "Can large eddy simulation techniques 
improve mesoscale rich ocean models ?"

-- 

MI