[MITgcm-support] Hydrostatic as grid approaches isotropic?

[Jody Klymak]

Thanks Max,

As is often the case, making a vanilla test suite helped me find my  
embarrassing error.

If anyone cares, I'd set K_z = 1000 for X<20 km in my code  
directory.   Worked great for absorbing internal waves in my 2000-km  
domain.  Not so good when I set dx = 5 m and my domain was less than  
15 km wide.

Sorry for the chatter.

Cheers,  Jody



On Jul 20, 2010, at  10:38 AM, Maxim Nikurashin wrote:

> Hi Jody,
>
> I am running simulations of internal tide generation from rough  
> topography which seem to be similar to what you do. I don't really  
> know why internal wave speed changes the way you describe it.  
> Interestingly, the wave speed changes with resolution by the same  
> factor of 10. I would expect that mode-1 is very large-scale and  
> well hydrostatic so that it should not be really affected by a  
> change in resolution from 50m to 5m or by running the model in non- 
> hydrostatic mode. I would suggest to run an experiment with dx=100m  
> and see if the wave speed changes again compared to dx=50m  
> simulation, but now by a factor of 2. If it always changes linearly  
> with resolution there must be something wrong with the way you setup  
> the simulation or estimate the wave speed.
>
> I could take a look at your experiment setup if you sent me your  
> files.
>
> All experiments that I run are in non-hydrostatic mode and I varied  
> both horizontal and vertical resolution. Large-scale internal tides  
> in my simulations radiate upward away from topography and have phase  
> line slopes, and therefore phase speeds, consistent with linear  
> theory estimates. Parameters from the data file from one of my  
> simulations are attached below.
>
> Cheers,
> Max.
>
>
> gravity = 9.81,
> gBaro   = 9.81,
> rigidLid = .TRUE.,
> # implicitFreeSurface=.FALSE.,
> nonHydrostatic = .TRUE.,
> staggerTimeStep = .TRUE.,
> saltStepping  = .FALSE.,
> tempAdvScheme = 77,
> hFacMin=0.1,
> &
>
> # Elliptic solver parameters
> &PARM02
> cg2dMaxIters       = 1000,
> cg2dTargetResidual = 1.E-10,
> cg3dMaxIters       = 50,
> cg3dTargetResidual = 1.E-10,
> &
>
> # Time stepping parameters
> &PARM03
>
> niter0 = 0,
> nTimeSteps  =   8640,
> deltaT      =    20.,
> dumpFreq    =  7200.,
> monitorFreq = 86400.,
> abEps       =    0.1,
> pChkptFreq  = 86400.,
> chkptFreq   =    0.0,
> &
>
> # Gridding parameters
> &PARM04
> usingCartesianGrid=.TRUE.,
> usingSphericalPolarGrid=.FALSE.,
> delX = 120*50,
> delY = 120*50,
> delRFile = 'delZ.init',
> &
>
>
>
>
>
> Jody Klymak wrote:
>> Hi again,
>>
>> Any thoughts on this?  Does anyone have a working near-isotropic  
>> setup that they could share the data file for?
>>
>> Thanks,  Jody
>>
>> On Jul 12, 2010, at  15:25 PM, Jody Klymak wrote:
>>
>>>
>>> Hi All,
>>>
>>> I have been banging my head against a wall with a simulation where  
>>> dz \approx 2 m and dx \approx 5 m (there is some telescoping away  
>>> from my topography and with depth).  I was running with  
>>> nonHydrostatic=.FALSE.  I expected mode-1 internal waves to zip  
>>> along at 1 m/s, but the fastest I was getting was 0.1 m/s.  I  
>>> thought it was my stratification etc etc.
>>>
>>> Then, or fun, I changed dx to 50 m.  Now I get 1 m/s mode-1 waves  
>>> and all is fine.  Is this a known feature of the code?  No doubt  
>>> an effect I should have learnt about somewhere...
>>>
>>> I include the pressure solving parts of my data file; maybe I'm  
>>> doing something wrong in here.  Note I use linear free surface  
>>> because I use Orlanski BCs. (ahem, though I really don't as I have  
>>> a big sponge in there.  I really only use the Orlanski code to set  
>>> OBNu, OBNv, etc, so if going to a non-linear surface works with  
>>> OBCs then I can make the effort).
>>>
>>> Thanks for any pointers....
>>>
>>> Cheers,  Jody
>>>
>>>
>>> gravity=9.81,
>>> gBaro=9.81,
>>> rigidLid=.FALSE.,
>>> implicitFreeSurface=.TRUE.,
>>> eosType='LINEAR',
>>> nonHydrostatic=.FALSE.,
>>> # minimum cell fraction.  This reduces steppiness..
>>> hFacMin=0.1,
>>> # implicSurfPress=0.5,
>>> # implicDiv2DFlow=0.5,
>>> # nonlinFreeSurf=3,
>>> # hFacInf=0.2,
>>> # hFacSup=1.8,
>>> #  exactConserv=.TRUE.,
>>> implicitDiffusion=.TRUE.
>>> implicitViscosity=.TRUE.
>>> # Superbee on:
>>> tempAdvScheme=77,
>>> staggerTimeStep=.TRUE.,
>>>
>>>
>>>
>>>
>>> -- 
>>> Jody Klymak
>>> http://web.uvic.ca/~jklymak/
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> MITgcm-support mailing list
>>> MITgcm-support at mitgcm.org
>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>
>> -- 
>> Jody Klymak
>> http://web.uvic.ca/~jklymak/
>>
>>
>>
>>
>>
>> _______________________________________________
>> MITgcm-support mailing list
>> MITgcm-support at mitgcm.org
>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>
>
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support

--
Jody Klymak
http://web.uvic.ca/~jklymak/