Jim Cowie wrote:
> I'm not sure if this is the correct venue for this issue, but we are having
> a problem running METRO (3.2.1) on a few sites. The one thing the sites seem
> to have in common is a rather thick asphalt layers on top of concrete. When
> METRo runs, we get the following message:
>
> ---------------------------------------------------
>
> EXECUTION : METRO_MODEL module: start execution
> EXECUTION : Start sending data to METRo core
> DEBUT SETCONSTPHYS
> FIN SETCONSTPHYS
> GRILLE ROUTINE START
> Numerical stability test failed
> for grid level 22
> Please increase the tickness of your
> layer, especially the cement if present
> STOP : Fatal error in METRo physical model.
>
> ----------------------------------------------------
>
> We can make this message go away if we increase the concrete thickness or
> decrease the asphalt thickness. However, this is arbitrary and I would
> rather have some additional guidance on layer thicknesses.
>
> I do not see any guidelines in the METRo documentation on minimum or
> maximum number of layers or layer thickness. Is this information
> documented somewhere?
>
> I have attached the example XML files for this case.
>
> Thank you for your attention,
>
> jim
>
>
Hi Jim,
The problem with this configuration is numeric stability (as written in
the error message).
Before throwing this error, METRo was producing NaN as outpout. See bug
7737 on Gna!
https://gna.org/bugs/?7737
This was fixed in the METRo release 3.0.1 in December 2006.
The problem is that if a layer with a good thermal conductivity is too
thin, METRo does not have enough layers in it to resolve the thermal
balance equation in one timestep. It is a well know problem in NWP, as
you might know, and it is called the CFL condition. See:
http://en.wikipedia.org/wiki/Courant%E2%80%93Friedrichs%E2%80%93Lewy_condition
The workaround is to do like you did: increase the tickness of concrete.
Sorry, there is no other fix and, even if we would fix METRo to process
your specific case, there would still be configuration that would raise
this error.
It is hard to give a guideline with real numbers to respect this
condition. It is why the error message is given at runtime. Depending on
the deepness of the layer (METRo as more layers at the surface), his
tickness and his type, the value will differ.
I have added a note in the METRo documentation regarding this. It is here:
http://documentation.wikia.com/wiki/Input_station_%28METRo%29#Layer_description
Does it answer your question?
Best regards,
Miguel
--
Miguel Tremblay
Physicien - Physicist
Centre météorologique canadien - Canadian meteorological centre (CMC)
Environnement Canada - Environment Canada
http://www.ec.gc.ca/
2121 Trans-Canada N. Suite 228 Téléphone/Phone: 514-421-4729
Dorval, Québec Fax: 514-421-4679
CANADA H9P 1J3 courriel/email: [email protected]
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