[MITgcm-support] Temperature undershoots using scheme 77 and GM

[David Ferreira]

Christopher,
Don't think anyone answered to you... In any case,  you should look at
the option:
#define  GAD_SMOLARKIEWICZ_HACK in GAD_OPTIONS.h
(there a clear comment coming with it)
I used it for a couple of passive tracers going negative, and it worked 
fine.
You'll need to  edit gad_calc_rhs.F to change the tracer number to apply 
it to
temperature (and/or salinity).
Cheers,
david



Christopher L. Wolfe wrote:
> Hi all,
>
> I'm running a low resolution (dx = 80 km) basin scale model and I'm 
> finding that my abyss is getting filled with water that's colder than 
> any surface water by .001 to .01 degrees. I'm using a linear equation 
> of state, no salt, no sea-ice, nothing fancy. I'm using advection 
> scheme 77 and GM in skew-flux form. Scheme 77 is not supposed to be 
> able to generate local interior maxima and GM is not supposed to be 
> able to create new water masses, so I'm at a loss as to what's causing 
> the undershoots. The problem seems to get worse at low diffusivities. 
> I use small (1e-5) isotropic Laplacian diffusivity, which would be 
> unstable if I wasn't using a flux limiter ... but I am. I run a 
> high-resolution version of the model with everything the same but no 
> GM and don't get any undershoots, so I suspect GM.
>
> Any thoughts as to what could be causing these undershoots?
>
> I'm using the latest version of the OS7MP scheme. My data and 
> data.gmredi files are included below.
>
> Thanks,
> Christopher
>
> data:
> # ====================
> # | Model parameters |
> # ====================
> #
> # Continuous equation parameters
>  &PARM01
>  tRef=-9.9, -9.9, -9.9, -9.9, -9.9, -9.9, -9.9
>       -9.9, -9.9, -9.9, -9.9, -9.9, -9.9, -9.9
>       -9.9, -9.9, -9.9, -9.9, -9.9, -9.9,
>  viscAh=10E3,
>  viscAz=0.25E-3,
>  no_slip_sides=.TRUE.,
>  no_slip_bottom=.FALSE.,
>  diffK4T=0.E9,
>  diffKhT=0.8E-4,
>  diffKzT=0.8E-4,
>  f0=-1.3683e-04,
>  beta=3.4208e-11,
>  tAlpha=2.E-4,
>  sBeta =0.,
>  gravity=10.,
>  rhoConst=1000.,
>  rhoNil=1000.,
>  heatCapacity_Cp=3900.,
>  rigidLid=.FALSE.,
>  implicitFreeSurface=.TRUE.,
>  saltAdvection=.FALSE.,
>  saltForcing=.FALSE.,
>  saltStepping=.FALSE.,
>  eosType='LINEAR',
>  nonHydrostatic=.FALSE.,
>  momAdvection=.TRUE.,
>  implicitViscosity=.TRUE.,
>  implicitDiffusion=.TRUE.,
>  ivdc_kappa=10.,
>  readBinaryPrec=64,
>  tempAdvScheme=7,
>  staggerTimeStep=.TRUE.,
>  bottomDragLinear=1.1135E-3,
>  debugLevel=-1,
>  useJamartWetPoints=.TRUE.,
>  useSingleCpuIo=.TRUE.,
>  &
>
> # Elliptic solver parameters
>  &PARM02
>  cg2dMaxIters=400,
>  cg2dTargetResidual=4.E-7,
>  cg3dMaxIters=400,
>  cg3dTargetResidual=4.E-7,
>  &
>
> # Time stepping parameters
>  &PARM03
>  nIter0=0,
>  nTimeSteps=3155760,
>  deltaT=4000,
>  abEps=0.1,
> # write out every 50 years
>  pChkptFreq=1.57788e9,
>  chkptFreq=1.57788e8,
>  dumpFreq=1.57788e9,
>  monitorFreq=1.57788e7,
>  tauThetaClimRelax=764400.,
>  cAdjFreq=0,
>  pickupStrictlyMatch=.FALSE.,
>  &
>
> # Gridding parameters
>  &PARM04
>  usingCartesianGrid=.TRUE.,
>  usingSphericalPolarGrid=.FALSE.,
>  dXspacing=80.e3,
>  dYspacing=80.e3
>  delZ=  12.0505,  14.9159,  18.4328,  22.7337,  27.9692,
>         34.3067,  41.9245,  51.0025,  61.7057,  74.1598,
>         88.4181, 104.4189, 121.9376, 140.5412, 159.5568,
>        178.0710, 194.9769, 209.0770, 219.2372, 224.5642
>  &
>
> # Input datasets
>  &PARM05
>  thetaClimFile='N85_SST.bin',
>  bathyFile='topo_two_noeddy.bin',
>  zonalWindFile='windx_two.weakeq',
>  meridWindFile=,
>  &
>
>
> data.gmredi:
>  &GM_PARM01
>   GM_background_K    = 0.9e+3,
>   GM_taper_scheme    = 'gkw91',
>   GM_maxSlope        = 1.e-2,
>   GM_Kmin_horiz      = 50.,
>   GM_Scrit           = 4.e-3,
>   GM_Sd              = 1.e-3,
>  &
>
>
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