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<<  Why do different results come from the same CCM3 code with d, http://bb.cgd.ucar.edu//viewtopic.php?t=23 >>

PosteratmocePostedSat Oct 09, 2004 5:29 am MDT, http://bb.cgd.ucar.edu//viewtopic.php?p=61#61
Message: Why do different results come from the same CCM3 code with different platform? 
<br />
<br />   
<br />  I've found a strange thing recently, i.e., the model
<br />results are quite different with the same both CCM3
<br />code and data set running in different SGI platform,
<br />one is on origin300, and the other is one sgi3800. 
<br /> I wonder where these conflications come
<br />from. Can anybody help me? Thanks in advance.

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<<  What is the COURLIM: *** Courant limit exceeded message?, http://bb.cgd.ucar.edu//viewtopic.php?t=22 >>

PosterpjrPostedFri Oct 08, 2004 10:34 pm MDT, http://bb.cgd.ucar.edu//viewtopic.php?p=60#60
Message: The spectral form of the equations of motion in CAM can become unstable when wind speeds become very strong. This situation is quite similar to the instability present in many finite difference schemes. The first analysis of the instability was performed by Courant Friedrichs and Levy in 1928. CAM will attempt to remove the instability when the winds would cause the model to go unstable. The algorithm is described in the users guide in the section on horizontal diffusion.
<br />
<br />A "Courant limit exceeded" message is issued whenever the algorithm is employed.
<br />
<br />There are two reasons I am aware of that trigger the limiter:
<br />
<br />1) the wind fields can get extremely strong in the middle atmosphere at the winter pole. This is a natural phenoma and occurs in the real world as well as the model. The limiter will kick in under these circumstances and reduce the wind speed to maintain stability. This is a perfectly normal occurance, and nothing to wo!
rry about.
<br />
<br />2) If there is an instability generated by any other aspect of the  model (for instance you might have introduced a bug), then it can amplify, and occasionally the Courant limiter will begin firing,  The model will soon halt (something will go terribly wrong)  You may see other manifestations of such an instability (ie other warning messages will begin appearing).
<br />
<br />Phil Rasch

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<<  How to report a bug in CAM, http://bb.cgd.ucar.edu//viewtopic.php?t=21 >>

PosterjmccaaPostedFri Oct 08, 2004 5:18 pm MDT, http://bb.cgd.ucar.edu//viewtopic.php?p=58#58
Message: We're working on the installation of bug tracking software for CAM, but in the mean time, you can report bugs in the Troubleshooting forum. If you do so, please make sure you include at least the following information:
<br />
<br />1. The version of CAM you used.
<br />2. The operating system on which you ran. 
<br />3. The compilers you used, including exact version numbers.
<br />4. The version numbers of any external libraries used (e.g. netcdf, mpich)
<br />5. The steps necessary to produce the problem.  At a minimum, these should include the arguments you gave to the configure command and the build-namelist command.
<br />
<br />If your interested in facilitating a fix for your bug, you should also consider reading the following general bug writing guidelines:
<br />http://bugs.cgd.ucar.edu/bugwritinghelp.html

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