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

Jody Klymak jklymak at uvic.ca
Wed May 7 18:02:36 EDT 2014


Hi guys,

Its not just shallower (and weaker) convection in the mixed layer?

Cheers,   Jody


On May 7, 2014, at  14:52 PM, Nicolas Grisouard <nicolas.grisouard at stanford.edu> wrote:

> Hi,
> 
> We must be talking about something different. The isopycnal slope I was referring to (weren't you?) is in the mixed layer, outcropping near y = -60 and dropping by 500 m within one horizontal grid cell: 50 km? If yes, that's a 1% slope, which is actually fairly steep. And it looks like it could be more, resolution permitting.
> 
> But if the PV is negative everywhere, I stand corrected.
> 
> Cheers,
> Nico.
> 
> On Wed 07 May 2014 02:27:34 PM PDT, Ryan Abernathey wrote:
>> Nico,
>> 
>> Interesting suggestion, but I don't think that's what's going on. Keep
>> in mind that the aspect ratio is tiny for this domain. That "steep"
>> isopycnal still extends over ~2000 km in the horizontal. The slope is
>> ~0.002. Relative vorticity is completely negligible here, and the PV
>> is everywhere negative.
>> 
>> -Ryan
>> 
>> 
>> On Wed, May 7, 2014 at 4:51 PM, Nicolas Grisouard
>> <nicolas.grisouard at stanford.edu
>> <mailto:nicolas.grisouard at stanford.edu>> wrote:
>> 
>>    Hi,
>> 
>>    Your isopycnal slopes there look very steep, but the image is very
>>    squeezed too. Could it be symmetric instability? It's not supposed
>>    to happen at these scales, but other mixed layer instabilities are
>>    probably inhibited by your 2D configuration so, why not? What's
>>    the sign of the PV there?
>> 
>>    Nico.
>> 
>> 
>>    On Wed 07 May 2014 12:57:26 PM PDT, Ryan Abernathey wrote:
>> 
>>        Thanks for all your suggestions.
>>        I tried turning on convective adjustment with
>>        ivdc_kappa=1.0,
>>        in my data file. I also enabled
>>        #define ALLOW_GGL90_SMOOTH
>>        in GGL90_OPTIONS.h
>> 
>>        It looks like the high values of W went down a little bit over the
>>        slope, a slight improvement. So I guess I am satisfied that,
>>        as Sonia
>>        put it, the solution is not "pretty" but is physically correct.
>> 
>>        I am still worried about the "stripes" of high and low W
>>        within the
>>        mixed layer between -60 and -50.
>> 
>>        Thanks again,
>>        Ryan
>> 
>> 
>> 
>>        On Wed, May 7, 2014 at 3:14 PM, David Ferreira <dfer at mit.edu
>>        <mailto:dfer at mit.edu>
>>        <mailto:dfer at mit.edu <mailto:dfer at mit.edu>>> wrote:
>> 
>>            Patrick's right, you need to have some convection with
>>        ggl90, but
>>            in case it's not enough: have you tried activating the
>>        smoother in
>>            ggl90 ? Might help too.
>>            david
>> 
>> 
>> 
>>            On 5/7/14 7:52 PM, Patrick Heimbach wrote:
>> 
>>                Ryan,
>> 
>>                yes, switching on convective adjustment is still
>>            advised in conjunction with ggl90 (in contrast to KPP
>>            where the non-local term Gamma should take care of this).
>> 
>>                Cheers
>>                p.
>> 
>>                On May 7, 2014, at 2:43 PM, Ryan
>>            Abernathey<ryan.abernathey at __gmail.com
>>            <mailto:ryan.abernathey at gmail.com>>
>>             <mailto:ryan.abernathey at gmail.__com
>>            <mailto:ryan.abernathey at gmail.com>>  wrote:
>> 
>>                    Thanks for all the helpful suggestions everyone!
>>                    I am now convinced that this isn't as "unphysical"
>>                as I thought.
>> 
>>                    In response to Christopher's suggestions, does
>>                anyone know whether I should have convective
>>                adjustment active together with GGL90? I know for KPP
>>                you are supposed to turn off all convective
>>                adjustment. Is that also the case for GGL?
>> 
>>                    Thanks again,
>>                    Ryan
>> 
>> 
>>                    On Wed, May 7, 2014 at 2:10 PM, Christopher L. P.
>>                Wolfe<christopher.wolfe at __stonybrook.edu
>>                <mailto:christopher.wolfe at stonybrook.edu>>
>>                 <mailto:christopher.wolfe at __stonybrook.edu
>>                <mailto:christopher.wolfe at stonybrook.edu>>  wrote:
>> 
>> 
>>                    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
>>                <mailto:ryan.abernathey at gmail.com>>
>>                 <mailto:ryan.abernathey at gmail.__com
>>                <mailto: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
>>                    <mailto:ryan.abernathey at gmail.com>>
>>                     <mailto: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)
>>                        ...
>> 
>> 
>> 
>>                    <W.png>_________________________________________________
>> 
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>>                ---
>>                Patrick Heimbach |heimbach at mit.edu
>>            <mailto:heimbach at mit.edu>  <mailto:heimbach at mit.edu
>>            <mailto:heimbach at mit.edu>> |http://www.mit.edu/~heimbach
>> 
>>                MIT | EAPS 54-1420 | 77 Massachusetts Ave | Cambridge
>>            MA 02139 USA
>>                FON+1-617-253-5259 <tel:%2B1-617-253-5259>
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>> 
>>    --
>>    --
>>    Nicolas Grisouard - Postdoctoral Scholar
>>    Stanford School of Earth Sciences
>>    473 via Ortega - room M11
>>    Stanford, CA 94305-4216
>>    Dept. fax: (+1) 650-498-5099 <tel:%28%2B1%29%20650-498-5099>
>>    Office Skype ID: nicolas.grisouard
>>    http://nicolas.grisouard.free.__fr<http://nicolas.grisouard.free.fr>
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> --
> Nicolas Grisouard - Postdoctoral Scholar
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> 473 via Ortega - room M11
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> Office Skype ID: nicolas.grisouard
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