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--></style></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt'>Hi everyone, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>The subject title sounds crazy but I did encounter this problem. I set up a high-resolution experiment (1~2 km for grid size in x-y, and 10m in z) and initialized it with linear stratification. The boundaries are Orlanski with net flow balanced. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Initially I used deltaT=60s but the code blew up with NaNs due to CFL condition. Then I decrease deltaT to 30s, the run could come to a normal end, but SSH increased/decreased to unreasonable values at Orlanski boundaries. I then used deltaT=5s, and SSH seemed to have smaller anomalies, but still blew up at boundaries. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>It seems that decreasing deltaT is the right way to ensure proper SSH behavior, and this did work for some cases with other kinds of initial stratifications. So I further decreased deltaT to 2s, but then I got much higher SSH blowups at boundaries than the case with deltaT=5s. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>According to this old post </span><a href="http://mailman.mitgcm.org/pipermail/mitgcm-support/2013-January/008122.html">http://mailman.mitgcm.org/pipermail/mitgcm-support/2013-January/008122.html</a> , this might be related to viscAhGrid, which is already used in my model and is calculated as below: <o:p></o:p></p><p class=MsoNormal>viscAh = 0.25*L**2*viscAhGrid/deltaT<o:p></o:p></p><p class=MsoNormal>The formula above shows that decreasing deltaT increases viscAh. What is confusing to me is that decreasing deltaT can give me both better or worse results. I assume this is related to viscAhGrid, but there might be other SSH instability issues that matter (Orlanski, etc). <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I have included the data file below. Really appreciate any help on this problem.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks,<o:p></o:p></p><p class=MsoNormal>Yilang<o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># ====================<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># | Model parameters |<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># ====================<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>#<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># Continuous equation parameters<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &PARM01<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> Tref = 50*-1.9,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> Sref = 34.0000, 34.0612, 34.1224, 34.1837, 34.2449, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>34.3061, 34.3673, 34.4286, 34.4898, 34.5510, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>34.6122, 34.6735, 34.7347, 34.7959, 34.8571, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>34.9184, 34.9796, 35.0408, 35.1020, 35.1633, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>35.2245, 35.2857, 35.3469, 35.4082, 35.4694, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>35.5306, 35.5918, 35.6531, 35.7143, 35.7755, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>35.8367, 35.8980, 35.9592, 36.0204, 36.0816, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>36.1429, 36.2041, 36.2653, 36.3265, 36.3878, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>36.4490, 36.5102, 36.5714, 36.6327, 36.6939, <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>36.7551, 36.8163, 36.8776, 36.9388, 37.0000,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> viscAz=1.E-3,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># viscAh=10.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> viscAhGrid=1.E-4,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> no_slip_sides=.FALSE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> no_slip_bottom=.FALSE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> diffKhT=0.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> diffKzT=1.E-6,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> diffKhS=0.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> diffKzS=1.E-6,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> bottomDragQuadratic=2.5E-3,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> eosType='JMD95Z', <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> HeatCapacity_cp = 3974.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> rhoConst=1030.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> rhoNil=1030.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> gravity=9.81,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> convertFW2Salt = 33.4,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> rigidLid=.FALSE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> implicitFreeSurface=.TRUE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> exactConserv=.TRUE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> hFacMin=0.05,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> nonHydrostatic=.FALSE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> readBinaryPrec=64,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> implicitDiffusion = .TRUE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> implicitViscosity = .TRUE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>saltAdvScheme=33,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>saltVertAdvScheme =33,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>tempAdvScheme=33,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>tempVertAdvScheme=33,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>staggerTimeStep=.TRUE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># useCDScheme = .TRUE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># Elliptic solver parameters<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &PARM02<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> cg2dMaxIters=1000,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> cg2dTargetResidual=1.E-13,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> cg3dMaxIters=400,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> cg3dTargetResidual=1.E-13,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># Time stepping parameters<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &PARM03<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> nIter0=0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> nTimeSteps=1728000,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> deltaT=2.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> abEps=0.1,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> cAdjFreq = 0.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># tauCD = 400000.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> pChkptFreq=1728000.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> chkptFreq=0.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> dumpFreq=432000.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> taveFreq=0.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> monitorFreq=36000.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> monitorSelect=2,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># Gridding parameters<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &PARM04<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> usingSphericalPolarGrid=.TRUE.,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> ygOrigin = -80.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> delXfile='dxfile.bin',<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> delYfile='dyfile.bin',<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> delZ=50*10.0,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># Input datasets<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &PARM05<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> bathyFile='bathy.box',<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># hydrogThetaFile='temp_3d_end_state.bin',<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># hydrogSaltFile='salt_3d_end_state.bin',<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># uVelInitFile='u_3d_end_state.bin',<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'># vVelInitFile='v_3d_end_state.bin',<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> &<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>