Base elevation problem

Any WPS problems/questions that might not fall into the other topics in this category

Base elevation problem

Postby swandoyo » Wed Oct 08, 2008 10:44 am

When I compare the base elevation of the center location(middle of the domain, 49.682039, -126.123555) with google earth, I always find differences and in complex terrain the difference as high as 500m. Is this because of the adjusment during terrain height interpolation and smoothing?
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Re: Base elevation problem

Postby PBLer » Wed Oct 08, 2008 11:01 am

Its probably due to a combination of interpolation, smoothing, and your model grid size. What is the size of your grid spacing? I've seen terrain height differences of over 1 km in regions of complex terrain. Unfortunately, WRF needs to run with a smoothed topography because it struggles over steep terrain. This is an outstanding issue that needs more attention.
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Re: Base elevation problem

Postby swandoyo » Wed Oct 08, 2008 11:09 am

The first nest of my domain is 30km and the second nest is 10km, and yes in that location, the terrain gradient is around 700m in 7km radius. Is there anyway around that problem? if I refine the domain to 1 or 4 km, the WRf run will be time consuming right? or I can have a domain spacing that differ than the solver domain?
Thanks a bunch for the reponse,
Swan
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Re: Base elevation problem

Postby PBLer » Wed Oct 08, 2008 12:09 pm

Going down to 1 or 4 km grid spacing will certainly help resolve your terrain and should help minimize the large differences you are seeing. If you are trying to accurately simulate gap flows, valley circulations, or mountain waves, you should definitely increase your resolution but of course, it will be much more time consuming.

Also, when you begin to resolve the steep slopes, you might run into other problems like spurious rain:

viewtopic.php?f=9&t=306

that thread has some more discussion on the issues of simulating flows over steep topography. Posting that link is not meant to deter your efforts. Just be aware of some possible errors you may encounter with high resolution simulations over complex topography.

good luck.
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Re: Base elevation problem

Postby swandoyo » Tue Oct 14, 2008 11:33 am

Many thanks,
At least now I know the problem that is basically a model limitation.

Regards,
Swan
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