[Wrf-users] Comparing U,V 10 meters to observations

Gary Lackmann gary at ncsu.edu
Tue Jan 26 19:39:17 MST 2010

Juan, Josh and all,

I have always (perhaps incorrectly) viewed the model 10-m winds as being 
related to the average over a model time step. In other words, if one is 
running with a 30 s time step, an average from four successive output 
times would be needed to compare to 2-min data from ASOS, for example. I 
understand, but haven't yet tried, that time averaging options are 
available for WRF output, and this could be the way to best handle the 
situation. Perhaps someone who has tried (or developed) that capability 
could chime in?

Hacker, Joshua (Josh) (CIV) wrote:

> Apologies to those who know this better than I do, but this is an 
> interesting question…
> Unless you do something fancy, the WRF outputs instantaneous 
> grid-point values, regardless of your output interval. Those values 
> are filtered non-trivially by some function of implicit and explicit 
> diffusion in the model (think physics, damping, time and space 
> discretization, etc). Therefore there is no one answer to your question.
> In practice (I believe) most people just compare directly to 10-min 
> averaged wind obs (WMO standard), or 2-min averaged wind obs (USA) but 
> in my opinion 2 minutes is usually too short to be fair.
> One approach to getting at the averaging in the model is through data 
> assimilation and statistical consideration of observation error levels 
> when the error may be dominated by representativeness error 
> (difference between scales represented in obs and model). Others have 
> looked in spectral space to get an idea of the averaging scales.
> The other thing that you might consider, if you have the data to do 
> it, is to compare WRF forecasts with obs averaged over many different 
> time lengths (or alternatively band-pass filtered). Then you can get a 
> more complete picture of what time scales it can or cannot predict 
> with skill, and decide whether it is doing what you hope.
> That said, I’d be interested in hearing any other comments from the 
> community and especially our verification gurus – is there any 
> “conventional” wisdom or rules of thumb that folks are using or that 
> have recently shown promise, empirically? Have I missed something?
> Sorry that there is no simple answer.
> Josh
> ------------------------------------------------------------------------
> *From:* wrf-users-bounces at ucar.edu [mailto:wrf-users-bounces at ucar.edu] 
> *On Behalf Of *Juan Gonzalez
> *Sent:* Tuesday, January 26, 2010 12:33 PM
> *To:* wrf-users at ucar.edu
> *Subject:* [Wrf-users] Comparing U,V 10 meters to observations
> Hi everyone,
> I am interested on validating the WRF 10m wind forecast with 
> observational data. I would like to know what is the corresponding 
> average scale for the WRF 10m winds, that is, do the correspond to 
> 1-minute, 10-minute average winds or what kind of average, if any?
> My WRF configuration outputs wind every 3 hours.
> Thanks for your help,
> Juan Gonzalez
> -- 
> Juan O. Gonzalez
> Research Assistant - Caribbean Integrated Coastal Ocean Observing System
> Graduate Student - Physical Oceanography
> Marine Sciences Department
> University of Puerto Rico - Mayaguez Campus
>Wrf-users mailing list
>Wrf-users at ucar.edu

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