[MITgcm-support] Help me get rid of my noise!

Wed May 7 14:10:52 EDT 2014

My guess that you’re seeing hydrostatic convection. You don’t seem to have set either cAdjFreq or ivdc_kappa and my understanding is that they both default to zero. So, your model’s trying to do convection through the momentum equations and the convective scale is smaller than your grid spacing (hydrostatic convection runs to the grid scale).

Christopher

On May 7, 2014, at 1:20 PM, Ryan Abernathey <ryan.abernathey at gmail.com> wrote:

> I guess my image didn't make it through on that last email.
> 
> 
> 
> On Wed, May 7, 2014 at 1:11 PM, Ryan Abernathey <ryan.abernathey at gmail.com> wrote:
> Hello MITgcm Support Group,
> 
> I am running a 2D model (depth and latitude) in a Southern Ocean configuration. I am trying to eliminate what appears to be unphysical grid-scale noise in my W field--columns of alternately very high and low W. This is a snapshot of W after 5 years of spinup. This pattern is steady in time.
> 
> As you can see, the noise is concentrated mainly (but not exclusively) over the shelf break. A possibly related issue is that my cg2d solver is relatively far from convergence:
> cg2d: Sum(rhs),rhsMax =  -5.46186194609888E-05  6.64557830841732E-02
> 
> My model is 0.5 degree resolution in latitude, meaning that it is relatively high resolution compared to the tutorials (e.g. ideal_2D_oce), but of course it has no eddies or any temporal variability at all, since it is 2D. This puts it in an unknown [at least to me] parameter regime.
> 
> I have tried cranking the lateral viscosity (both laplacian and biharmonic) up as high as they will go. I have enabled both linear and quadratic bottom drag. I am NOT using the CD scheme; the noise was much worse with it enabled. I am NOT using KPP but rather GGL90. (I tried with KPP and it was not very different.)
> 
> I would appreciate any suggestions you have about how to get rid of this noise and achieve smooth fields.
> 
> Thanks,
> Ryan
> 
> ####### data file ##########
>  &PARM01
>  useAreaViscLength=.FALSE.,
>  viscAr=1.0E-03,
>  viscA4=1e12,
>  viscAh=1e5,
>  tempAdvScheme=77,
> # KrT fields are read in from a file
>  diffKrT=0.0E-5,
>  diffKhT=0.0,
>  diffK4T=0.0,
>  staggerTimeStep=.TRUE.,
> # initial vertical profiles of T and S
>  tRef=44*0.0,
>  sRef=44*35.0,
> # equation of state
>  eosType='LINEAR',
>  rhonil=1035.,
>  eosType='LINEAR',
>  tAlpha=2.000000E-04,
>  sBeta=0.000000E+00,
>  saltStepping=.FALSE.,
> # boundary conditions
>  no_slip_sides=.FALSE.,
>  no_slip_bottom=.TRUE.,
> # needed for points above the U sponge layer (shelf)
>  bottomDragLinear=1.E-3,
>  bottomDragQuadratic = 0.0012
> # additional drag is done with RBCS
> # physical parameters
>  gravity=9.810000E+00,
> # implicit diffusion and convective adjustment
>  implicitDiffusion=.TRUE.,
>  implicitViscosity=.TRUE.,
>  implicitFreeSurface=.TRUE.,
> # exact volume conservation
> # exactConserv=.TRUE.,
> # C-V scheme for Coriolis term
>  useCDscheme=.FALSE.,
> # partial cells for smooth topography
>  hFacMin=5.000000E-02,
> # file IO stuff
>  readBinaryPrec=64,
>  useSingleCpuIO=.TRUE.,
>  debugLevel=1,
>  &
> # elliptic solver parameters
>  &PARM02
>  cg2dMaxIters=500,
>  cg2dTargetResidual=1E-09,
>  &
> # timestepping parameters
>  &PARM03
>  nIter0=0000172800,
> # nTimeSteps=1000,
> # nTimeSteps=12961,
>  nTimeSteps=345600,
> # deltaT=3600.0,
> # deltaT=2400.,
> # deltaT=1800.0,
>  deltaT=900.0,
>  abEps=0.1,
> # needed for sea ice
>  forcing_In_AB = .FALSE.,
>  ChkptFreq=31104000.
>  pChkptFreq=311040000.,
>  taveFreq=311040000.0,
>  dumpFreq=31104000.,
>  monitorFreq=2592000.0,
>  tauThetaClimRelax=2592000.0,
>  dumpInitAndLast=.TRUE.,
>  pickupStrictlyMatch=.FALSE.,
>  &
> # gridding parameters
>  &PARM04
>  usingSphericalPolarGrid=.TRUE.,
>  delX=0.5,
>  delY=100*0.5,
>  xgOrigin=0.,
>  ygOrigin=-80.,
>  delR=10., 10., 10., 10., 10., 10., 10., 12., 14.,
>   16.,   19.,   22.,   26.,   30.,   36.,   42.,   50.,   60.,
>   72.,   85.,  100.,  120.,  140.,  166.,  200.,  200.,  200.,
>   200.,  200.,  200.,  200.,  200.,  200.,  200.,  200.,  200.,
>   200.,  200.,  200.,  200.,  200.,  200.,  200.,  200.
>  &
> # Input datasets
>  &PARM05
>  bathyFile='bathyFile_shelf_2Dchan.bin',
>  zonalWindFile='zonalWindFile.bin',
>  thetaClimFile='thetaClimFile_WOA98_2Dchan.bin',
>  diffKrFile='diffKrFile_nosponge_2Dchan.bin',
>  hydrogThetaFile='hydrogThetaFile_WOA98_2Dchan.bin',
>  hydrogSaltFile='hydrogSaltFile_WOA98_2Dchan.bin',
>  &
> 
> ########## data.pkg ##############
>  &PACKAGES
>   useMNC         = .TRUE.,
>   useGMREDI      = .TRUE.,
>   useGGL90       = .TRUE.,
>   useRBCS        = .TRUE.,
>  &
> 
> ######## data.gmredi ##############
>  &GM_PARM01
>   GM_MNC             = .FALSE,
>   GM_AdvForm         = .TRUE.,
>   GM_UseBVP          = .TRUE.,
>   GM_background_K    = 2000,
>   GM_isopycK         = 2000,
>   GM_Kmin_horiz      = 50,
>   GM_taper_scheme    = 'dm95',
>   GM_BVP_ModeNumber  = 1,
>   GM_BVP_cMin        = .1,
>  &end
> 
> ########### data.ggl90 ############
>  &GGL90_PARM01
>  GGL90writeState=.FALSE.,
>  GGL90TKEmin = 1.e-7,
>  mxlMaxFlag=2,
>  GGL90mixingLengthMin=3.,
>  &
> 
> 
> ############ SIZE.h ##############
> ...
>       PARAMETER (
>      &           sNx =   1,
>      &           sNy = 100,
>      &           OLx =   4,
>      &           OLy =   4,
>      &           nSx =   1,
>      &           nSy =   1,
>      &           nPx =   1,
>      &           nPy =   1,
>      &           Nx  = sNx*nSx*nPx,
>      &           Ny  = sNy*nSy*nPy,
>      &           Nr  =  44)
> ...
> 
> 
> <W.png>_______________________________________________
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