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

[Ryan Abernathey]

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)
...
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20140507/96b6a075/attachment-0001.htm>