[MITgcm-support] Too short time step ?!

[Menemenlis, Dimitris (3248)]

For horizontal viscosity, you can also try the Leith scheme, which attempts to choose a viscosity that is just right for damping grid scale noise while maintaining a realistic energy cascade that extends as close as possible to your grid's Nyquist wavenumber:

 viscAh=0.,
 viscAhGrid=0.,
 viscC2Leith=0.,
 viscA4=0.,
 useFullLeith=.TRUE.
 viscC4Leith=2.0,
 viscC4Leithd=2.0,

On Jul 6, 2010, at 9:11 PM, Matthew Mazloff wrote:

> Hi Zhang,
> 
> You can turn up  viscAh and also add some diffusivity to stabalize the  
> model run.
> 
> For your domain something like
>  viscAz =1.E-4,
>  viscAh =1.E1,
>  viscA4 =1.E9,
>  diffKhT=1.E0,
>  diffKzT=1.E-5,
>  diffKhS=1.E0,
>  diffKzS=1.E-5,
>  bottomDragQuadratic=1.E-3,
> 
>  deltaTmom   = 1200.0,
>  deltaTtracer= 1200.0,
> 
> may be better
> 
> -Matt
> 
> 
> 
> 
> On Jul 6, 2010, at 7:40 PM, 张正光 wrote:
> 
>> Dear mitgcm-support team,
>>        Hi, I'm Zhang.
>>        I'm modeling the overflow, now I'm running a idealized case,  
>> but I have to set my time step very short (dt=120s) in order to run  
>> my case, otherwise, it will go crazy or shut down.
>>        I'v checked the "Numerical Stability Criteria", which told  
>> me I can use a much longer time step.
>>        I'm confused, and my case need to be integrated for  
>> 30-50year, so use dt=120s will cost too much computer time. What can  
>> I do to use a longer time step?
>>        My grid size: dx=25km, dy=50km, dz=100m (uniform grid)
>>        and I think give you my "data" file maybe better:
>> 
>> # ====================
>> # | Model parameters |
>> # ====================
>> #
>> # Continuous equation parameters
>> &PARM01
>> tRef=40*20.,
>> sRef=40*35.,
>> viscA4=0.0E4,
>> viscAh=1.E-2,
>> viscAz=1.E-3,
>> no_slip_sides=.TRUE.,
>> no_slip_bottom=.TRUE.,
>> diffK4T=0.E4,
>> diffKhT=0.E-2,
>> diffKzT=0.E-3,
>> diffK4S=0.E4,
>> diffKhS=0.E-2,
>> diffKzS=0.E-5,
>> f0=0.e-5,
>> beta=0.E-11,
>> rhonil=1035.,
>> rhoConstFresh=1000.,
>> eosType = 'JMD95Z',
>> rigidLid=.FALSE.,
>> implicitFreeSurface=.TRUE.,
>> hFacMin=0.05,
>> nonHydrostatic=.TRUE.,
>> readBinaryPrec=64,
>> #- not safe to use globalFiles in multi-processors runs
>> #globalFiles=.TRUE.,
>> bottomDragLinear=0.E-4,
>> bottomDragQuadratic=0.003,
>> tempAdvScheme=33,
>> &
>> 
>> # Elliptic solver parameters
>> &PARM02
>> cg2dMaxIters=300,
>> cg2dTargetResidual=1.E-13,
>> cg3dMaxIters=400,
>> cg3dTargetResidual=1.E-8,
>> &
>> 
>> # Time stepping parameters
>> &PARM03
>> niter0=0,
>> nTimeSteps=10000,
>> #nTimeSteps=20000,
>> deltaT=600.0,
>> abEps=0.01,
>> pChkptFreq=120000000.0,
>> chkptFreq=600000.0,
>> dumpFreq=600000.0,
>> #dumpFreq=120000.0,
>> taveFreq=600000.0,
>> tauThetaClimRelax=100000.0,
>> monitorFreq=6000.,
>> # staggerTimeStep=.TRUE.,
>> &
>> 
>> # Gridding parameters
>> &PARM04
>> usingCartesianGrid=.TRUE.,
>> usingSphericalPolarGrid=.FALSE.,
>> delXfile='dx.bin',
>> delYfile='dy.bin',
>> # dYspacing=200.,
>> delZ=40*100.0,
>> &
>> 
>> # Input datasets
>> &PARM05
>> bathyFile='topog.slope',
>> hydrogThetaFile='T.init',
>> surfQfile='Qnet.forcing',
>> thetaClimFile='SST.bin',
>> diffKrFile='diffK.bin'
>> #hydrogThetaFile='T.pickup',
>> #hydrogSaltFile='S.pikup',
>> #uVelInitFile='U.pickup',
>> #vVelInitFile='V.pickup',
>> #pSurfInitFile='Eta.pickup',
>> &
>> <ATT00001.txt>
> 
> 
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