[Wrf-users] CFL criterion - general question

[Jan Harlass]

Hi Elena,

another thing you could try is to add:
smooth_cg_topo = .true.
under &domains in the namelist when you run real. This smoothes the 
model topography to match the low resolution topography that comes with 
the driving data, if CFL happens along boundary zones. If CFL occurs 
near complex terrain, you may try to set epssm=0.2 ( up to 0.5) to see 
if that helps.
[from http://www.mmm.ucar.edu/wrf/users/FAQ.html]

Also remember to scale your time step with the maximum map factor of 
your domain. This value is written out in the log files of real.exe. The 
time step is then: dt (sec) = 6*dx (km) / (maximum map factor)

All the best!

     Jan



Am 01.11.2012 06:51, schrieb Elena Maria Pison San Pedro:
>
> Hello,
>
> I've remarked that sometimes when I run a simulation (WRF3.4) I got 
> messages saying " x points exceeded cfl=2 at time..." _but the 
> simulation run to completion_.
>
> How can this affect the results? What can I do to solve this 
> instabilities, run a higher time step?
>
> Thanks a lot in advance!
>
> Best regards,
>
> Elena
>
> Elena Pison San Pedro
>
> M.Sc. in Atmospheric Sciences
>
>
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-- 
-----------------------------------------------------------
Dipl.-Met. Jan Harlaß
FB1, FE Maritime Meteorologie, PhD-Student
Helmholtz-Zentrum für Ozeanforschung Kiel (GEOMAR)
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Alte Botanik Raum 61
24105 Kiel, Germany
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Tel. +49-431-600-4034
Fax  +49-431-600-4052
jharlass at geomar.de
www.geomar.de/~jharlass-e
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