[MITgcm-support] Too short time step ?!

[张正光]

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',
 &
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