[MITgcm-support] Help me get rid of my noise!
Sonya Legg
sonya.legg at noaa.gov
Wed May 7 14:49:19 EDT 2014
Hi Ryan,
I would concurr with Nicolas and Christopher that what you are probably
seeing is poorly resolved convectively driven motion. There are perhaps
two different types of motion - the downward motion along the slope,
with a compensating return flow just above, which is taking the dense
water from the shelf into the deep ocean, and then the more vertically
aligned up/down motion in the upper ocean offshore from the shelfbreak,
where isopycnals are vertical and convection is driven by the local
buoyancy loss. Convective adjustment may help with the latter but not
the former - and you would want to keep the effect of the downslope
motion on the tracer fields. May just have to accept that things don't
look pretty (i.e. smooth) at coarse resolution even if physically correct.
Sonya
On 05/07/2014 01:20 PM, Ryan Abernathey 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 <mailto: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)
> ...
>
>
>
>
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> MITgcm-support at mitgcm.org
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