[MITgcm-support] Runaway gyre south of Australia in global simulation

[Christopher L. Wolfe]

Hi modelers,

I'm running a quasi-global simulation at 1 x 1 degree resolution on a lat-long grid which spans 80 S to 80 N. Bathymetry, wind stress, and freshwater flux are taken from OCCA (Forget 2010), using the monthly mean forcing repeated ad infinitum. The temperature forcing is done by relaxing the surface temperature back to the monthly mean surface temperature from OCCA over a time scale of a month. The initial conditions are OCCA's January. The idea is to run under these forcings for a long time to see what kind of equilibrium solutions they give.

Everything looks pretty reasonable for the first 200 years of integration, but then a massive gyre (800 Sv) develops just south of Australia and persists for the rest of the integration (at least out to 500 years). The gyre circulates clockwise and has its maximum transport near the *eastern* boundary, just offshore of South Australia. The very large values of the streamfunction extend to the mid-ocean ridge located around 90 E; after that it becomes difficult to distinguish from the Southwest Indian gyre. I can send interested parties a plot of the barotropic streamfunction. (I'll refrain from sending it to the whole mailing list since it's >200 kB.)

I've had similar problems using surface forcing from the World Ocean Atlas and da Silva.

While I don't expect the model to necessarily stay close to the initial conditions, this behavior strikes me as unphysical and I've never heard of it popping up in other global ocean circulation experiments. It seems like it must be some sort numerical instability, but I can't figure out where it originates. Has anyone seen anything like this before? Any hints on how to fix it?

I'm attaching the relevant data files below.

Thanks,
Christopher

-----------------------------------------------------------
Dr. Christopher L. Wolfe              	   858-534-4560
Climate, Atmospheric Science, and Physical Oceanography
Scripps Institution of Oceanography, UCSD  clwolfe at ucsd.edu
-----------------------------------------------------------

data:
#
# ******************************
# Model parameters
# Continuous equation parameters
# ******************************
 &PARM01
 tRef= 24.0 , 23.0 , 22.0 , 21.0 , 20.0 ,
       19.0 , 18.0 , 17.0 , 16.0 , 15.0 ,
       14.0 , 13.0 , 12.0 , 11.0 , 10.0 ,
        9.0 ,  8.0 ,  7.0 ,  6.0,   5.0 ,
        4.0 ,  3.0 ,  2.0 ,
 sRef= 34.65, 34.75, 34.82, 34.87, 34.90,
       34.90, 34.86, 34.78, 34.69, 34.60,
       34.58, 34.62, 34.68, 34.72, 34.73,
       34.74, 34.73, 34.73, 34.72, 34.72,
       34.71, 34.70, 34.69,
 no_slip_sides=.TRUE.,
 no_slip_bottom=.TRUE.,
 viscAz=1.E-3,
 viscAh=1.E4,
 diffKhT=1.E2,
 diffKzT=1.E-5,
 diffKhS=1.E2,
 diffKzS=1.E-5,
 beta=1.E-11,
 tAlpha=2.E-4,
 sBeta =7.4E-4,
 gravity=9.81,
 gBaro=9.81,
 rigidLid=.FALSE.,
 implicitFreeSurface=.TRUE.,
 eosType='JMD95P',
 readBinaryPrec=64,
 writeBinaryPrec=64,
 staggerTimeStep=.TRUE.,
 saltAdvScheme=7,
 saltStepping=.TRUE.,
 salt_EvPrRn=0,
 convertFW2Salt=-1,
 tempAdvScheme=7,
 tempStepping=.TRUE.,
 momStepping=.TRUE.,
 implicitDiffusion=.TRUE.,
 implicitViscosity=.TRUE.,
 allowFreezing=.TRUE.,
 debugLevel=-1,
 useJamartWetPoints=.TRUE.,
 useSingleCpuIo=.TRUE.,
 bottomDragQuadratic=0.002,
 &

# **************************
# Elliptic solver parameters
# **************************
 &PARM02
 cg2dMaxIters=1000,
 cg2dTargetResidual=1.E-13,
 &

# ************************
# Time stepping parameters
# ************************
 &PARM03
 nIter0=0,
 nTimeSteps=1095000,
 deltaTmom=1800.0,
 deltaTtracer=14400.0,
 deltaTfreesurf=14400.0,
 cAdjFreq=0.,
 abEps=0.1,
 pChkptFreq = 1.5768e10,
 chkptFreq  = 1.5768e9,
 dumpFreq   = 1.5768e9,
 monitorFreq= 1.5768e7,
 tauThetaClimRelax=2592000.,
 dumpInitAndLast=.TRUE.,
 periodicExternalForcing=.TRUE.,
 externForcingPeriod=2628000,
 externForcingCycle=31536000,
 &

# *******************
# Gridding parameters
# *******************
 &PARM04
 usingSphericalPolarGrid=.TRUE.,
 delX=360*1.E0,
 delY=160*1.E0,
 delZ=10.,10.,15.,20.,20.,25.,35.,50.,75.,100.,150.,200.,275.,350.,415.,450.,500.,500.,500.,500.,500.,500.,500.,
 ygOrigin=-80.,
 &
# **********
# Data Files
# **********
 &PARM05
 bathyFile='bathymetry.bin',
 hydrogThetaFile='T_init.bin',
 hydrogSaltFile='S_init.bin',
 uVelInitFile='U_init.bin',
 vVelInitFile='V_init.bin',
 pSurfInitFile='Eta_init.bin',
 zonalWindFile='occa_taux.bin',
 meridWindFile='occa_tauy.bin',
 thetaClimFile='occa_sst.bin',
 EmPmRFile='occa_EmPmR.bin',
 checkIniTemp=.false.,
 &

data.gmredi:
 &GM_PARM01
  GM_background_K    = 1000,
  GM_taper_scheme    = 'dm95',
  GM_AdvForm         = .TRUE.,
  GM_UseBVP          = .TRUE.,
  GM_InMomAsStress   = .FALSE.,
  GM_BVP_ModeNumber  = 2,
  GM_BVP_cMin        = .1,
 &

data.pkg:
 &PACKAGES
 useKPP	      = .TRUE.,
 useGMRedi    = .TRUE.,
 useSeaice    = .FALSE.,
 useDiagnostics = .TRUE.,
 useMNC = .FALSE.,
 &


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