[MITgcm-support] viscAh & viscAz?

[Baylor Fox-Kemper]

Hi Van Thinh,
   Are you using non-hydrostatic mode?  If so, Leith and Smagorinsky  
are not yet implemented, and you can only use viscAh or viscA4.
   If you are using hydrostatic mode, and you are at O(10m)  
resolution, it is probably most sensible to be using the Smagorinsky  
scheme.  You should be able to run it with no other viscosities.  If  
you are having trouble with noise, you might try adding some  
biharmonic viscosity.
   Try this to get started:

  &PARM01
  viscAr=5.E -5,
  # This is harmonic Smagorinsky Coefficient
  # 0.2-0.9=value from 3-d turbulence theory; Smagorinsky (1993)
  # 2.2-4=stable oceanic values (Griffies and Hallberg, 2000)
  # 1.0 smag is approximately the same as 1.85 leith+leithd
  # for this grid spacing
  viscC2Smag=1.0,
  viscC4Smag=1.0,
  # This is the max Viscosity used, be it Smag or Leith, and it scales
  # with grid size and timestep
  viscAhGridMax=0.5,
  viscA4GridMax=0.5,

   implicitDiffusion=.TRUE.,
   implicitViscosity=.TRUE.,

# These two might be particularly useful, depending on your problem
   usejamartwetpoints=.TRUE.,
   staggerTimeStep=.TRUE.,

# You should stick with the 33, it reduces noise.
   tempAdvScheme=33,
   saltAdvScheme=33,
   nonHydrostatic=.FALSE.,
  &

You can play with the values of the Smagorinsky coefficients to see  
what effect they have.

If you are using nonhydrostatic mode, let me know (I am overdue on  
setting up the variable viscosity for nonhydrostatic mode anyway!)
   Cheers,
    -Baylor

On Jun 8, 2006, at 3:37 PM, Van Thinh Nguyen wrote:

> Dear all,
>
> In oder to reduce the noises, I am playing with parameters viscAh &  
> viscAz, so I have some questions, could someone please help me?
>
> 1. From the documentation, we can have two ways to set viscAh:
>    a. By estimating velocity & grid scale
>    b. By using viscAhReMax and/or viscC2Smag (or maybe combine with  
> Leith
>       viscosity)
>   So, I understand that when I use option b) then I don't need to set
>   viscAh or viscAz in &PARM01, is that correct?
>
> 2. Here are some options in data file:
>
>  &PARM01
> #
>  viscAz=1.E-5,
>  viscAh=1.E-5,
>  tempAdvScheme=33,
>
>  viscA4=0.E12,
>  diffK4T=0.E4,
>  diffKhT=1.E-5,
>  diffKzT=1.E-5,
>  diffK4S=0.E4,
>  diffKhS=1.E-5,
>  diffKzS=1.E-5,
>
>  implicitDiffusion=.TRUE.,
>  implicitViscosity=.TRUE.,
>
>  viscC2leith=1.,
>  viscC2leithd=1.,
> ##
>  &
>  &PARM04
>
>  viscC2Gmag=4.,
>  viscAhGridMax=0.5,
>
>  &
>
> I even try to increase viscAh & viscAz (to 1.E-1), as well as  
> increase viscC2leith=viscC2leithd=1.
> but I still get noises.
> I know that you should know my simulation (problem &domain length  
> scale) related to grid space (dX=10m) & time step (1s). However, I  
> just wanna know
> that my above options are correct or anything in conflict.
>
> My problem has to be dealed with the range of viscAh=1.E-6 &  
> viscAz=1.E-6, but I got stuck in this simulation due to the noises.
>
> Thanks so much for your helps.
>
>
> Van Thinh
>
> -----------------------------------------------------
>
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