[MITgcm-support] viscAh & viscAz?

[Van Thinh Nguyen]

Hi Baylor,

When I run the non-hydrostatic mode with the option of Smagorinsky and 
Leith, the program had no warning or error, it just crashed after 1/2 
tidal period (22320 s), it happened the same when i played only with 
viscAh & viscAz (increased to 1.). And with the option of Smagorinsky & 
Leith, it shows a great reduce the noises with the low values of viscAh &
viscAz (10-5). So I'm not sure that Smagorinsky & Leith wouldn't work with 
non-hydrostatic?

In case to run non-hydrostatic mode with Smagorinsky and/or Leith, some 
works have to be implemented, could you please give me some hints which 
subroutines have to be concerned?

Thanks a lot!

Van Thinh

-------------------------------------------

On Fri, 9 Jun 2006, Baylor Fox-Kemper wrote:

> 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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