[MITgcm-support] Problems caused by Orlanski radiation boundary

[Lin Zhang]

Hi all,
I am simulating the evolution of 3D vortex in stratified fluid with MITgcm, and use Orlanski radiation open boundary,
and f=0.

In the first run, I give the initial U, V and theta (Salinity=35), which form a circular vortex, and the model runs well.
In the second run, I initialize U, V, theta with vertically tilted vortex, it runs well in the before 5000 steps, after that, the eta rises, to 10m at 10000steps.

In data.obcs, CMAX=0.45, cvelTimescale=2000, I tried to change cveltimescale to 1000, then the eta begin to rise after
8000 steps.

data file is:
# Model parameters
# Continuous equation parameters
 &PARM01
 tRef=40*20.,
 sRef=40*35.,
 viscAz=1.E-2,
 viscAh=4.E2,
 no_slip_sides=.FALSE.,
 no_slip_bottom=.TRUE.,
 diffKhT=4.E2,
 diffKzT=0,
 f0=0,
 beta=0,
 tAlpha=2.E-4,
 sBeta =0.,
 gravity=9.81,
 rigidLid=.FALSE.,
 implicitFreeSurface=.TRUE.,
 eosType='LINEAR',
 readBinaryPrec=64,
 &
# Elliptic solver parameters
 &PARM02
 cg2dMaxIters=1000,
 cg2dTargetResidual=1.E-13,
 &
# Time stepping parameters
 &PARM03
 nIter0=      20000,
 nTimeSteps = 10000, 
 deltaTmom=120.0,
 deltaTtracer=600.0,
 abEps=0.1,
 pChkptFreq=6000000.0,
 chkptFreq=0.0,
 dumpFreq=300000.0,
 monitorFreq=1.,
 &
# Gridding parameters
 &PARM04
 usingCartesianGrid=.TRUE.,
 usingSphericalPolarGrid=.FALSE.,
# phiMin=0.,
 delX=101*6E3,
 delY=101*6E3,
 delZ=40*50.,
 &
 &PARM05
 bathyFile='topog.box',
 uVelInitFile='U_f0.init',
 vVelInitFile='V_f0.init',
 hydrogThetaFile='Theta_f0.init',
 hydrogSaltFile=,
 zonalWindFile=,
 meridWindFile=,
 &

Also, I tried nonhydrostatic case, the results is similar.

Thank you1
Lin
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