Deactivate Friction in idealized WRF

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Deactivate Friction in idealized WRF

Postby dakiesi » Fri Dec 29, 2017 1:36 pm


I am currently trying to simulate, what Schaer and Durran (1997) did in their simulation. I slightly changed some things like domain size but that should not alter the result too much.

It is actually not very complicated, but I am stuck with one thing: Schaer and Durran used a free-slip condition which I understand means no friction at the surface. How do I set the namelist settings to deactivate surface friction? I tried to use this guy's problem : viewtopic.php?f=9&t=119#p7593

I set isfflx = 2 but left sf_sfclay_physics=0 (no surface layer). Is it true that than there is no surface friction?

Thank in advance
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Joined: Sun Nov 26, 2017 11:27 am

Re: Deactivate Friction in idealized WRF

Postby moulin » Tue Jan 02, 2018 12:31 pm


From my experience in running idealized em_les case, setting sf_clay_physics=0 will get a free-slip boundary at the surface. the option isfflx = 2 will have no effect once sf_clay_physics is set to 0, since setting isfflx = 2:
use drag from sf_sfclay_physics and heat flux from tke_heat_flux with bl_pbl_physics=0.

quote from Readme.namelist.

I guess you will also get a free-slip boundary by setting isfflx = 0 and tke_drag_coefficient=0, since this option explicitly use tke_drag_coefficient to compute the drag at the surface. But I haven't try this way myself. You can also give it a shot :).

Hope it could help you.

Mou Lin
Wind Engineering and Renewable Energy Laboratory
École polytechnique fédérale de Lausanne
Posts: 3
Joined: Wed Mar 01, 2017 8:44 am

Re: Deactivate Friction in idealized WRF

Postby dakiesi » Wed Jan 03, 2018 2:38 pm

hey moulin,

thank you for your reply. I will give it try to run with sf_sfclay_physics=0. If that is not successfull, i will try it with the specified fluxes (tke_drag_coefficient and tke_heat_flux).

thanks again
Posts: 7
Joined: Sun Nov 26, 2017 11:27 am

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