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

Wed Jan 27 10:59:28 MST 2010

Thanks to all.

I will do some comparisons using the recommendations everyone gave and then
based on the outcome I will have a better idea of how the model behaves in
terms of the equivalent time averaging and take a final decision. My
interpretation was that the wind vectors were the instantaneous value for
the given time step and so I had doubts if any scale factor had to be used
to compare them to observed winds.

Juan

On Wed, Jan 27, 2010 at 12:21 PM, Jim Dudhia <dudhia at ucar.edu> wrote:

> 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* <wrf-users-bounces at ucar.edu> [*
> mailto:wrf-users-bounces at ucar.edu* <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* <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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-- 
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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