<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;">Please follow Dimitris’ recommendation. <div><br></div><div>Asynchronous timestepping has been used for long spinup simulations with coarse resolution.<div><br></div><div>The different timestep parameters do *not* mean that the model is stepped deltaTclock/deltaTtracer times, etc. Instead it means that say at time step two, the model time witll be 2*deltaTclock (used to determine when new forcing is to be read, etc), and the tracer equations will have been stepped 2 times with deltaTtracer, i.e. the tendencies are very small, when deltaTtracer is very small, and this means that it will not develop very much, e.g 0.002 sec. The seaice models use deltaTtracer as the default time step, unless you specify is explicitly, so the same applies.</div><div><br></div><div>Martin<br id="lineBreakAtBeginningOfMessage"><div><br><blockquote type="cite"><div>On 4. Sep 2024, at 03:51, Menemenlis, Dimitris (US 329B) <dimitris.menemenlis@jpl.nasa.gov> wrote:</div><br class="Apple-interchange-newline"><div>
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<div>from MITgcm/model/inc/PARAMS.h</div>
<div><br>
</div>
<div>C deltaT :: Default timestep ( s )</div>
<div>C deltaTClock :: Timestep used as model "clock". This determines the</div>
<div>C IO frequencies and is used in tagging output. It can</div>
<div>C be totally different to the dynamical time. Typically</div>
<div>C it will be the deep-water timestep for accelerated runs.</div>
<div>C Frequency of checkpointing and dumping of the model state</div>
<div>C are referenced to this clock. ( s )</div>
<div>C deltaTMom :: Timestep for momemtum equations ( s )</div>
<div>C dTtracerLev :: Timestep for tracer equations ( s ), function of level k</div>
<div><br>
</div>
<div>but I recommend that for your problem you just set deltaT so that you have:</div>
<div><br>
</div>
<div>deltaTClock = deltaTMom = dTracelLev = deltaT</div>
<div><br>
</div>
<div>D.</div>
<div><br>
</div>
<div><br>
<blockquote type="cite">
<div>On Sep 3, 2024, at 6:05 PM, 唐鸿 <tanghong22@mails.ucas.ac.cn> wrote:</div>
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<div><p><span style="font-family:Times New Roman;font-size:13px;">Dear MITgcm Support Team,</span>
</p><p><span style="font-family:Times New Roman;"><br>
</span></p><p><span style="font-family:Times New Roman;font-size:13px;">I hope this message finds you well.</span><span style="font-family:Times New Roman;">
<span style="font-size:14px;"></span><br>
</span></p><p><span style="font-family:Times New Roman;"><br>
</span></p><p><span style="font-family:Times New Roman;"><span style="font-family:Times New Roman;font-size:13px;">I am currently working on a simulation project using the MITgcm to study the dynamics of a lake, including the freezing process during winter. I have encountered
some confusion regarding the behavior of the model with respect to the parameters
</span><strong><span style="font-family:Times New Roman;font-size:13px;">deltaTtracer</span></strong><span style="font-family:Times New Roman;font-size:13px;">,
</span><strong><span style="font-family:Times New Roman;font-size:13px;">deltaTmom</span></strong><span style="font-family:Times New Roman;font-size:13px;">, and
</span><strong><span style="font-family:Times New Roman;font-size:13px;">deltaT</span></strong><strong><span style="font-family:Times New Roman;font-size:13px;">Clock</span></strong><span style="font-family:Times New Roman;font-size:13px;">, and I am seeking
your guidance.</span></span> </p><p><span style="font-family:Times New Roman;"><br>
</span></p><p><span style="font-family:Times New Roman;font-size:13px;">In my understanding, the model should operate as follows when given the settings:</span>
</p>
<ul>
<li><span style="font-family:Times New Roman;font-size:13px;">deltaTClock = 3600s</span>
</li><li><span style="font-family:Times New Roman;font-size:13px;">deltaTtracer = 1800s</span>
</li><li><span style="font-family:Times New Roman;font-size:13px;">deltaTmom = 100s</span>
</li></ul><p><span style="font-family:Times New Roman;font-size:13px;">I believed that over one deltaTClock period, the tracer equations would be updated twice, and the momentum equations would be updated 36 times.</span>
</p><p><span style="font-family:Times New Roman;font-size:13px;"><br>
</span></p><p><span style="font-family:Times New Roman;font-size:13px;">However, I have conducted two different simulations with the following configurations and results:</span>
</p>
<ol>
<li><p><span style="font-family:Times New Roman;font-size:13px;">First simulation configuration:</span>
</p>
<ul>
<li><span style="font-family:Times New Roman;font-size:13px;">nIter0 = 0</span> </li><li><span style="font-family:Times New Roman;font-size:13px;">nTimeSteps = 13199</span>
</li><li><span style="font-family:Times New Roman;font-size:13px;">deltaTClock = 3600s</span>
</li><li><span style="font-family:Times New Roman;font-size:13px;">deltaTmom = 0.00001s</span>
</li><li><span style="font-family:Times New Roman;font-size:13px;">deltaTtracer = 3600s</span>
</li></ul>
<strong><span style="font-family:Times New Roman;font-size:13px;"><span style="font-size:13px;">The resu</span><span style="font-size:13px;">lting ice_iceH output seemed more reasonable, with ice formation as expected.</span></span></strong>
</li><li><p><span style="font-family:Times New Roman;font-size:13px;">Second simulation configuration:</span>
</p>
<ul>
<li><span style="font-family:Times New Roman;font-size:13px;">nIter0 = 0</span> </li><li><span style="font-family:Times New Roman;font-size:13px;">nTimeSteps = 13199</span>
</li><li><span style="font-family:Times New Roman;font-size:13px;">deltaTClock = 3600s</span>
</li><li><span style="font-family:Times New Roman;font-size:13px;">deltaTmom = 0.001s</span>
</li><li><span style="font-family:Times New Roman;font-size:13px;">deltaTtracer = 1s</span>
</li></ul>
<strong><span style="font-family:Times New Roman;"><span style="font-size:13px;"><span style="font-size:13px;">Surprisingly, this simulation di</span><span style="font-size:13px;">d not produce any ice formation</span></span><span style="font-size:13px;">.</span></span></strong>
</li></ol><p><span style="font-family:Times New Roman;"><span style="font-size:13px;">The driving data spans from 2015-06-15 to 2016-12-15 with a time resolution of 3600 seconds.
</span><span style="font-size:13px;">Intuitively, I think that the si</span><span style="font-size:13px;">mulation resul</span><span style="font-size:13px;">ts s</span><span style="font-size:13px;"><span style="font-size:13px;">hould be the same for both configurations
</span><span style="font-size:13px;">, with only a difference in runtime</span><span style="font-size:13px;">.
</span></span><span style="font-size:13px;">I am puzzled by the behavior of these parameters, particularly deltaTtracer and deltaTmom, and how they actually take effect within the model.</span></span>
</p><p><span style="font-family:Times New Roman;"><br>
</span></p><p><span style="font-family:Times New Roman;"><span style="font-size:13px;">Could you please clarify how these parameters are supposed to function within the model, and whether my understanding aligns with the model's implementation?
</span><br>
</span></p><p><span style="font-family:Times New Roman;"><br>
</span></p>
<div><span style="font-family:Times New Roman;"></span><br class="webkit-block-placeholder">
</div><p><span style="font-family:Times New Roman;font-size:13px;">I would greatly appreciate any suggestions or guidance you could provide. I am really looking forward to your valuable insights and suggestions.</span>
</p><p><span style="font-family:Times New Roman;"><br>
</span></p><p><span style="font-family:Times New Roman;font-size:13px;">Best regards,</span>
<span style="font-family:Times New Roman;"><br>
</span></p><p><span style="font-family:Times New Roman;"><br>
</span></p><p><span style="font-family:Times New Roman;font-size:13px;">Hong Tang</span> </p>
<span style="font-family:Times New Roman;font-size:13px;">University of Chinese Academy of Chinese</span><br><p><br>
</p>
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</blockquote>
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