Hi Elena,<div><br></div><div>I have had the same thing happen. I don't know exactly how that affects the results, so when it has happened to me, I did not trust the results.</div><div><br></div><div>Yes, reducing the time step is the standard way to avoid CFL errors. There are some alternatives like using restart files: when CFLs appear, stop, go back a little way in time, use small time steps for a while, stop and continue forward using the larger timesteps. That is mostly done for very long runs like climate downscaling when it is not practical to use small timesteps for an entire run.</div>
<div><br></div><div>If CFLs always appear at the same coordinates such as a mountain peak, EPSSM can be adjusted or the grid changed.</div><div><br></div><div>If you need more information and detail about what I do to avoid CFL errors, I have some on my website: <a href="http://www.nusculus.com/wrf-errors">http://www.nusculus.com/wrf-errors</a></div>
<div><br></div><div>I don't claim to be an expert; I have simply suffered through a lot of bad WRF runs.</div><div><br></div><div>But most people just keep reducing the time step until the CFL errors go away.</div><div>
<br></div><div>Kevin<br><br><div class="gmail_quote">On Wed, Oct 31, 2012 at 11:51 PM, Elena Maria Pison San Pedro <span dir="ltr"><<a href="mailto:emp@dhi.com.sg" target="_blank">emp@dhi.com.sg</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div lang="EN-SG" link="blue" vlink="purple"><div><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">Hello,<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">I’ve remarked that sometimes when I run a simulation (WRF3.4) I got messages saying “ x points exceeded cfl=2 at time…” <u>but the simulation run to completion</u>.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><u></u> <u></u></span></p><p class="MsoNormal"><span><img width="1037" height="576" src="cid:image001.jpg@01CDB837.EDF30050"></span><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">How can this affect the results? What can I do to solve this instabilities, run a higher time step?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">Thanks a lot in advance!<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">Best regards,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">Elena<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><u></u> <u></u></span></p>
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