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<TITLE>Re: [Wrf-users] Experiences with high-resolution WRF-ARW</TITLE>
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<FONT FACE="Helvetica, Verdana, Arial"><SPAN STYLE='font-size:12.0px'>Eric,<BR>
<BR>
My experience is that high vertical resolutions severely limit the time step. For example, when running with 57 layers and the vertical resolution set to about 35 m at the surface and dx=18, 6, and 2 km for the 3 nested domains, I need timesteps of 30, 10, 3.33 sec, respectively. How far down the timestep has to go will also be a function of the weather conditions in the domain. If a frontal passage occurs, or deep convection, with strong vertical velocities, a shorter timestep is required.<BR>
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-Bill<BR>
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On 2/27/08 1:01 PM, "Kemp, Eric M." <Eric.Kemp@ngc.com> wrote:<BR>
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Dear wrf-users:<BR>
<BR>
My group is running WRF-ARW at high resolution (dx = 1 km) to simulate turbulence. <BR>
Recently we tried running at very high vertical resolution (dz ~= 12.5 m in the lowest<BR>
500 m of the domain), and encountered CFL errors with time steps as<BR>
low as 1/8 of a second. These runs used the 6th order diffusion<BR>
option from Knievel et al (2007), along with real terrain (area around<BR>
Albuquerque, NM) and physics (MYJ TKE, Noah land surface,<BR>
RRTM/Dudhia radiation, and WSM5 microphysics).<BR>
<BR>
Has anyone here run WRF at such fine resolution, and if so, what were<BR>
your experiences with the time step? The ARW documentation recommends<BR>
6 seconds for each kilometer of dx, ignoring the effect of vertical resolution. <BR>
Are there other settings that should be tuned?<BR>
<BR>
-Eric<BR>
<BR>
Eric M. Kemp<BR>
Meteorologist<BR>
Northrop Grumman Information Technology<BR>
Intelligence Group (TASC)<BR>
4801 Stonecroft Boulevard<BR>
Chantilly, VA 20151<BR>
(703) 633-8300 x7078 (lab)<BR>
(703) 633-8300 x8278 (office)<BR>
(703) 449-3400 (fax)<BR>
eric.kemp@ngc.com<BR>
<BR>
<BR>
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</SPAN></FONT></FONT><FONT FACE="Helvetica, Verdana, Arial"><SPAN STYLE='font-size:11.0px'>--------------------------------------------------------------------<BR>
<I>William I. Gustafson Jr.<BR>
</I>Atmospheric Science and Global Change Division<BR>
Pacific Northwest National Laboratory<BR>
3200 Q Ave., MSIN K9-30<BR>
Richland, WA 99352<BR>
(509)372-6110</SPAN><SPAN STYLE='font-size:12.0px'><BR>
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