[MITgcm-support] model unstability caused by increasing sea surface elevation(eta)

[Mohammadhossein Kharaghani]

?Hello MITgcm community

I have a simple model with three open boundaries in the north, east and west, and in this model that Tide is given to the model as a time series (including 8 components) up to 30 hours (more than one period).There is no problem in the topography and input data of open boundaries. However, sea surface elevation(eta) in my model rises quickly and greatly at all points from the start of running, thus, the model quickly becomes unstable. Griding and dimensions of the model are as follows:

The grid in the horizontal direction is equal to ten meters and in the vertical direction it has 14 layers of 0.5, 1 and 2 meters from the surface to the floor. The range of the model is as 1.18 km x 0.8 km and the maximum depth is 15 meters.

Best regards

MohammadHossein


Data file:

 &PARM01

 Tref = 21.084700, 21.020412, 20.977085, 20.948000, 20.928308, 20.914621, 20.896999, 20.885466, 20.877001, 20.870974, 20.864302, 20.859730, 20.857693, 20.853001,

 sRef= 41.913029, 41.911030, 41.909740, 41.908958, 41.908516, 41.908287, 41.908123, 41.908012, 41.907799, 41.907497 41.907089, 41.906998, 41.906975, 41.906933,

 viscAz=1.E-3,

 viscAh=1.E-2,

 no_slip_sides=.FALSE.,

 no_slip_bottom=.FALSE.,

 diffKhT=1.E-2,

 diffKzT=1.E-3,

 diffKhS=1.E-2,

 diffKzS=1.E-3,

# saltAdvScheme=4,

 f0=0.0,

 beta=0.E-11,

 eosType='LINEAR',

 tAlpha=2.E-4,

 sBeta =0.E-4,

 gravity=9.81,

 implicitFreeSurface=.TRUE.,

 rigidLid=.FALSE.

 implicitDiffusion=.FALSE.,

 exactConserv=.TRUE.,

 nonHydrostatic=.FALSE.,

 hFacMin=1.0,

 implicSurfPress=1.0,

 implicDiv2DFlow=1.0,

 nonlinFreeSurf=1,

 hFacInf=0.2,

 hFacSup=1.8,

 saltStepping = .FALSE.,

 tempStepping = .FALSE.,

#- not safe to use globalFiles in multi-processors runs

#globalFiles=.TRUE.,

 readBinaryPrec=64,

 writeBinaryPrec=64,

 writeStatePrec=64,

 &

# Elliptic solver parameters

 &PARM02

 cg2dMaxIters=500,

 cg2dTargetResidual=1.E-13,

 cg3dMaxIters=400,

 cg3dTargetResidual=1.E-13,

 &

# Time stepping parameters

 &PARM03

 nIter0=0,

 nTimeSteps=108000,

 deltaT=1.0,

 pChkptFreq=3600.,

 chkptFreq=0.,

 dumpFreq=3600,

 monitorFreq=1.,

 monitorSelect=2,

# for time dependent open boundary conditions, activate the following 3 lines:

   periodicExternalForcing=.TRUE.,

   externForcingPeriod=3600.,

   externForcingCycle =108000.,

 &

# Gridding parameters

 &PARM04

 usingCartesianGrid=.TRUE.,

 dySpacing=10.,

 dxSpacing=10.,

 delZ=0.5,0.5,0.5,0.5,0.5,0.5,1.0,1.0,1.0,1.0,2.0,2.0,2.0,2.0,

 &

# Input datasets

 &PARM05

 bathyFile='TopoKharg4',

 &


Data.obcs file

# Open boundaries

 &OBCS_PARM01

 OB_Jnorth =   118*-1,

 OB_Iwest  =   80*1,

 OB_Ieast  =   80*-1,

 useOBCSsponge = .TRUE.,

# This flag check and equalise topography across open boundaries:

 OBCSfixTopo = .FALSE.,

 useOBCSprescribe= .TRUE.,

  OBNuFile='OBNut.iwkharg_obcs',

  OBNvFile='OBNvt.iwkharg_obcs',

  OBWuFile='OBWut.iwkharg_obcs',

  OBWvFile='OBWvt.iwkharg_obcs',

  OBEuFile='OBEut.iwkharg_obcs',

  OBEvFile='OBEvt.iwkharg_obcs',

  OBEetaFile='OBEeta.iwkharg_obcs',

  OBNetaFile='OBNeta.iwkharg_obcs',

  OBWetaFile='OBWeta.iwkharg_obcs',

  OBCS_monitorFreq= 1.,

  OBCS_monSelect = 1,

 &

 &OBCS_PARM03

  spongeThickness= 10 ,

  Urelaxobcsinner= 1000,

  Vrelaxobcsinner= 1000,

  Urelaxobcsbound= 100,

  Vrelaxobcsbound= 100,

 &?

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