[MITgcm-support] Too short time step ?!

[Matthew Mazloff]

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>