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

Wed Jan 27 09:21:15 MST 2010

I think the advective time scale idea falls apart when the wind is  
light.
There I would just compare it with long enough time averages to remove  
gusts,
because it is an area mean,
Jimy

On Jan 27, 2010, at 9:05 AM, Michael McAtee wrote:

> Jimy,
>
> You indicated that "In cases of stronger winds the averaging time  
> can be considered equivalent to the advective time-scale across a  
> grid box..."   Does this relationship hold for light wind conditions  
> or is there some different relationship that applies.  I ask because  
> as you know the air quality community often makes comparisons of   
> model (WRF and MM5) 10-m wind to surface observations  for air  
> pollution events that usually occur in stagnate, light wind  
> conditions.
>
> Mike
>
> ___________________________
> Michael D. McAtee, Ph.D.
> Senior Project Engineer, Meteorological Satellite Systems
> The Aerospace Corporation
> 101 Nelson Drive
> Offutt, AFB, NE 68113-1023
> email:  michael.mcatee at aero.org
> Phone: (402) 292-1017
> Fax: (402) 291-3137
>
>
> From:	Jim Dudhia <dudhia at ucar.edu>
> To:	Ligia Bernardet <Ligia.Bernardet at noaa.gov>
> Cc:	wrf-users at ucar.edu, "Hacker, Joshua \(Josh\) \(CIV\)" <jphacker at nps.edu 
> >
> Date:	01/27/2010 09:21 AM
> Subject:	Re: [Wrf-users] Comparing U,V 10 meters to observations
> Sent by:	wrf-users-bounces at ucar.edu
>
>
>
>
> All,
> In cases of stronger winds the averaging time can be considered  
> equivalent
> to the advective time-scale across a grid box when looking at the  
> U10 and V10.
> So for a 4 km hurricane run with 40 m/s, it would be 4000/40=100  
> seconds
> which may be comparable with 1-minute averages,
> Jimy
>
> On Jan 27, 2010, at 8:12 AM, Ligia Bernardet wrote:
>
> Josh and Juan,
>
> I ran into this issue while trying to compare 10-m model wind  
> forecasts against hurricane maximum wind reports, which are also an  
> average over a few minutes.  There was no good solution.
>
> Having WRF output time series of variables at a grid point or time  
> series of statistical quantities (such as maximum winds) has been a  
> standing request to developers, and may be addressed at some point.
>
> I have talked to several hurricane modelers who, for research  
> purposes, output the model winds every time step to look at how much  
> it varies. Different authors got to different conclusions. Some  
> modelers noted that their model winds fluctuate a lot (and therefore  
> averaging is really necessary before comparing to obs), other noted  
> that their winds are pretty steady (and therefore direct comparison  
> to observations is not a problem).
>
> So, I think this is an outstanding issue. If others have experience  
> with this, I would also like to know more.
>
> Ligia
>
>
>
>
> On Jan 26, 2010, at 5:06 PM, 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
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