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

Nicolas Grisouard nicolas.grisouard at stanford.edu
Wed May 7 17:52:19 EDT 2014


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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>             <tel:%2B1-617-253-4464>  <tel:%2B1-617-253-4464>  | SKYPE
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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>
>     http://www.mendeley.com/__profiles/nicolas-grisouard/
>     <http://www.mendeley.com/profiles/nicolas-grisouard/>
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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
Office Skype ID: nicolas.grisouard
http://nicolas.grisouard.free.fr
http://www.mendeley.com/profiles/nicolas-grisouard/



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