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

[Matthew Mazloff]

I suspect your inflow
OBNvFile='OBNvt.iwkharg_obcs',
OBWuFile='OBWut.iwkharg_obcs',
OBEuFile='OBEut.iwkharg_obcs’,
doesn’t balance. 

You can use obcs tides, for example:
 tidalPeriod =  44714.16431337780, 43200.00001728000, 45570.05357245878, 43082.04528908103,
                86164.09057816206, 92949.63009971760, 86637.20483483445, 96726.08376243486
 OBSamFile='OBS_SWOT_TdlAmp_trans_Jan_2015v1.bin',
 OBWamFile='OBW_SWOT_TdlAmp_trans_Jan_2015v1.bin',
 OBNamFile='OBN_SWOT_TdlAmp_trans_Jan_2015v1.bin',
 OBSphFile='OBS_SWOT_TdlPhs_trans_Jan_2015v1.bin',
 OBWphFile='OBW_SWOT_TdlPhs_trans_Jan_2015v1.bin',
 OBNphFile='OBN_SWOT_TdlPhs_trans_Jan_2015v1.bin'

and separate tidal flow out. This may help you. It would also allow you to use
 useOBCSbalance=.TRUE.,

-Matt


> On Aug 23, 2022, at 11:43 AM, Mohammadhossein Kharaghani <m_kharaghani at civileng.iust.ac.ir> wrote:
> 
> ​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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