[MITgcm-support] Hydrostatic as grid approaches isotropic?

[Maxim Nikurashin]

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