[MITgcm-support] Modeling of the surface waves

[Jean-Michel Campin]

Hi George,

I don't know what is the SSH (eta field) you are expecting with this forcing,
but when setting:
>  useOBCSbalance=.TRUE.,
with the default OBCS_balanceFacE=1 & OBCS_balanceFacW=1,
the net Inflow/outflow through all OB (here E & W) is adjusted (corrected) 
to remain zero.
And may be this explains the small SSH variations you are getting.

There are few comments at the top of pkg/obcs/obcs_balance_flow.F
which explain what parameters OBCS_balanceFac_E,W,N,S are doing.

Cheers,
Jean-Michel

On Mon, Oct 29, 2012 at 09:33:11AM +0800, 王刚 wrote:
> 
> Dear all,
> 
>      I try to simulate the surface gravity waves in a small  water tank using non-hydrostatic model. The eastern boundary is sponge layers, and western boundary is prescribed periodical changing U and W. They are sinusoidal or cosinusoidal waves exponentially decayed with depth  [U=a*c*k*exp(k*z)*cos(k*x-sigma*t   and  w=-a*c*k*exp(k*z)*sin(k*x-sigma*t),   where  a=0.2m is the amplitude of sea lever，c=2m/s  is the phase velocity，k=2*pi/10m wavenumber，z=12.6m depth，sigma frequency]. However, the eta (sea surface lever) is very small (almost zero) in my result, and I can not find any clue of surface waves. Did I set wrong perameters?
> 
> . The following are my data 
> 
> # Continuous equation parameters
>  &PARM01
>  tRef =100*20,  
>  sRef = 100*10,
>  f0=0,           
>  viscAz=1.0E-6,
>  viscAh=1.0E-6,
>  no_slip_sides=.FALSE.,
>  no_slip_bottom=.FALSE.,
>  viscA4=0.E12,
>  diffKhT=1.44E-7,
>  diffKzT=1.44E-7,
> #diffK4T=5.E3,
>  diffKhS=1.44E-7,
>  diffKzS=1.44E-7,
>  beta=0.E-11,
>  tAlpha=2.E-4,    
>  sBeta =7.4E-4,
>  gravity=9.81,
>  gBaro=9.81,
>  rigidLid=.FALSE.,
>  nonHydrostatic=.TRUE.,
>  implicitFreeSurface=.TRUE.,
>  eosType='LINEAR',
>  readBinaryPrec=64,
> #- not safe to use globalFiles in multi-processors runs
> #globalFiles=.TRUE.,
>  writeBinaryPrec=64,
>  writeStatePrec=64,
> #saltStepping=.FALSE.,
>  hFacMin=0.1,
>  implicSurfPress=0.5,
>  implicDiv2DFlow=0.5,
> #nonlinFreeSurf=3,
> #hFacInf=0.2,
> #hFacSup=2.0,
>  exactConserv=.TRUE.
>  &
> 
> # Elliptic solver parameters
>  &PARM02
>  cg2dMaxIters=1000,
>  cg2dTargetResidual=1.E-10,
>  cg3dMaxIters=100,
>  cg3dTargetResidual=1.E-10,
>  &
> 
> # Time stepping parameters
>  &PARM03
>  niter0=0,
>  nTimeSteps=250000,
>  deltaT=0.02,
>  deltaTtracer=0.02,
>  abEps=0.0001,
>  pChkptFreq=500,
>  chkptFreq=500,
>  dumpFreq=1,
>  monitorFreq=0.1,
>  periodicExternalForcing=.TRUE.,
>  externForcingPeriod=0.02,
>  externForcingCycle=5,
>  &
> 
> # Gridding parameters
>  &PARM04
>  usingCartesianGrid=.TRUE.,
>  usingSphericalPolarGrid=.FALSE.,
>  delX=1000*0.5,
>  delY=5,
>  delZ=10*0.05,10*0.06,10*0.07,10*0.08,10*0.1,10*0.12,10*0.15,10*0.18,10*0.2,10*0.25,
> &
> 
> # Input datasets
>  &PARM05
>  hydrogThetaFile='T.init',
> #hydrogSaltFile='S.init',
>  bathyFile='topog',
>  &
> 
> 
>   , and data.obcs  
> 
>         
> # Open-boundaries
>  &OBCS_PARM01
>  OB_Ieast=-1,
>  OB_Iwest=1,
>  useOrlanskiEast =.TRUE.,
>  useOrlanskiWest =.FALSE.,
>  useOBCSbalance=.TRUE.,
>  useOBCSprescribe=.TRUE.,
> #useOBCSsponge=.TRUE.,
> #OBEuFile='uEast.bin',
>  OBWuFile='uWest.bin',
> #OBWwFile='wWest.bin',
> #OBWetaFile='etaWest.bin',
> &
> 
> &OBCS_PARM02
>  cmax=0.45D0,
>  cvelTimeScale=5.D0,
> &
>  
> # *****************************************
> # Sponge Layer Parameters.
> # *****************************************
>  &OBCS_PARM03
> # Urelaxobcsinner  = 0,
> #Urelaxobcsbound  = 5,
> #spongeThickness  = 20,
>  &
> # end of the parameters.

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