<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Dear Hong Tang,<div><br></div><div>since it is a lake I assume that the salinity is zero and you don’t have to worry about salinity advection (so you could set saltStepping = .FALSE. to save some time), but your temperature advection will be done by the default central differences (tempAdvScheme = 2), which requires stabilisation by diffusion, which is unset and will default to zero.</div><div><br></div><div>So either you change your advection scheme to one with numerical diffusion to stabiliize it, e.g.</div><div> tempAdvScheme = 3, 30, 33 or 7 (have a look ad GAD.h for all options)</div><div><br></div><div>or (and?) you need to set diffKhT to some value > 0</div><div><br></div><div>and your diffKrT (vertical diffusion) should also be non-zero. With 1m vertical resolution, the vertical cfl will probably be the limiting factor for the timestep (monitor adv_cfl_wvel, etc.)</div><div><br></div><div>Martin</div><div><div><div><br><blockquote type="cite"><div>On 1. Aug 2024, at 16:48, 唐鸿 <tanghong22@mails.ucas.ac.cn> wrote:</div><br class="Apple-interchange-newline"><div><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><p>
<span style="font-family:Times New Roman;">Dear MITgcm Support Team,</span>
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<span style="font-family:Times New Roman;">I hope this message finds you well.</span><span style="font-family:Times New Roman;"> </span>
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<span style="font-family:Times New Roman;">I am currently working on a simulation project using the </span><span style="font-family:Times New Roman;">MITgcm to study the dynamic processes of a lake situated on the Tibetan Plateau, which experiences freezing during winter. The lake, located at an altitude of 4200m with a depth of 28m and a maximum width of 38km, presents unique challenges due to the strong radiation on the plateau that leads to noticeable warming of the water beneath the ice.</span>
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<span style="font-family:Times New Roman;">I am writing to seek your expert advice as I have encountered <strong>significant numerical instability</strong> in my simulations despite my efforts to adjust model parameters. My current setup is that the horizontal grid size is <strong>500m</strong> and the vertical grid size is <strong>1m</strong>. I have modified the model time step and drive data time to <strong>100s</strong>, but I still encounter serious numerical instability.</span>
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<span style="font-family:Times New Roman;"> I have attached my </span><code class="inlineCode___uUrJ9"><span style="font-family:Times New Roman;"><strong>data</strong></span></code><span style="font-family:Times New Roman;"><strong> file</strong>, which contains the configuration parameters of my model setup.</span><span style="font-family:Times New Roman;"></span><span style="white-space:pre;"> </span>
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<span style="color:#6a9955;"># ====================</span>
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<span style="color:#6a9955;"># | Model parameters |</span>
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<span style="color:#6a9955;"># ====================</span>
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<span style="color:#6a9955;">#</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span><span style="color:#9cdcfe;">PARM01</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">tRef</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;"> </span><span style="color:#b5cea8;">10</span><span style="color:#d4d4d4;">*</span><span style="color:#b5cea8;">11</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">sRef</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;"> </span><span style="color:#b5cea8;">10</span><span style="color:#d4d4d4;">*</span><span style="color:#b5cea8;">0.27</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">no_slip_sides</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;">.</span><span style="color:#569cd6;">FALSE</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">no_slip_bottom</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;">.</span><span style="color:#569cd6;">TRUE</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">viscAh</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">1.E-4</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">viscAr</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">1.E-4</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">HeatCapacity_Cp</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">3986</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">rhoConstFresh</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">1000</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">rhoNil</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">1000</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">eosType</span><span style="color:#d4d4d4;">=</span><span style="color:#ce9178;">'JMD95Z'</span><span style="color:#cccccc;">,</span>
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<span style="color:#6a9955;"># </span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">nonHydrostatic</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;">.</span><span style="color:#569cd6;">TRUE</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">rigidLid</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;">.</span><span style="color:#569cd6;">TRUE</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">implicitFreeSurface</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;">.</span><span style="color:#569cd6;">FALSE</span><span style="color:#cccccc;">.,</span>
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<span style="color:#6a9955;">#</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">useCoriolis</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;">.</span><span style="color:#569cd6;">FALSE</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">use3dCoriolis</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;">.</span><span style="color:#569cd6;">FALSE</span><span style="color:#cccccc;">.,</span>
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<span style="color:#6a9955;">#</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">useSingleCpuIO</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;">.</span><span style="color:#569cd6;">TRUE</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">readBinaryPrec</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">32</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">writeBinaryPrec</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">32</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span>
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<span style="color:#6a9955;"># Elliptic solver parameters</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span><span style="color:#9cdcfe;">PARM02</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">cg2dMaxIters</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">700</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">cg3dMaxIters</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">100</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">cg2dTargetResidual</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">1.E-7</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">cg3dTargetResidual</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">1.E-7</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">cg2dUseMinResSol</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">1</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span>
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<span style="color:#6a9955;"># Time stepping parameters</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span><span style="color:#9cdcfe;">PARM03</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">abEps</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">0.1</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">deltaT</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">100</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">nIter0</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">0</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">nTimeSteps</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">315361</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">dumpFreq</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">86400</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">chkPtFreq</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">2592000</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">pChkptFreq</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">8640000</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">monitorFreq</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">100</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span>
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<span style="color:#6a9955;"># Gridding parameters</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span><span style="color:#9cdcfe;">PARM04</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">usingCartesianGrid</span><span style="color:#d4d4d4;">=</span><span style="color:#cccccc;">.</span><span style="color:#569cd6;">TRUE</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">dXspacing</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">500</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">dYspacing</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">500</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">delR</span><span style="color:#d4d4d4;">=</span><span style="color:#b5cea8;">10</span><span style="color:#d4d4d4;">*</span><span style="color:#b5cea8;">1</span><span style="color:#cccccc;">.,</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span>
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<span style="color:#6a9955;"># Input datasets</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span><span style="color:#9cdcfe;">PARM05</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">bathyFile</span><span style="color:#d4d4d4;">=</span><span style="color:#ce9178;">'Bathy_500m.bin'</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#9cdcfe;">the_run_name</span><span style="color:#d4d4d4;">=</span><span style="color:#ce9178;">'Ngoring_LakeTest_HH'</span><span style="color:#cccccc;">,</span>
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<span style="color:#cccccc;"> </span><span style="color:#d4d4d4;">&</span>
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<span style="font-family:Times New Roman;">I would greatly appreciate any suggestions or guidance you could provide to improve the numerical stability of my simulation. Thank you very much for considering my request. I look forward to your valuable insights and suggestions.</span>
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<span style="font-family:Times New Roman;">Best regards,</span>
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<span style="font-family:Times New Roman;">Hong Tang</span>
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<span style="font-family:Times New Roman;">University of Chinese Academy of Sciences<br>
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</p>_______________________________________________<br>MITgcm-support mailing list<br>MITgcm-support@mitgcm.org<br>http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support<br></div></blockquote></div><br></div></div></body></html>