[gradsusr] Question about why the wind vectors barbs not showing up for the 0-6 KM Shear difference

[Jeff Duda]

The reason you are only approximating the 0-6 km shear is because you
are substituting the 6 km AGL winds for the 500 mb flow.  Since most
datasets are isobaric and don't offer data on a constant height AGL
surface, it's common to use the 500 mb flow since 500 mb is reasonably
close to 6 km AGL for most locations over the central and eastern US.
It does remain an approximation since it may be up to a few thousand
feet off.  In my experience viewing observed soundings, during the
warm season the 6 km AGL level is typically a little above 500 mb (in
the 450-500 mb layer).  There is a Grads script out there that can use
linear interpolation in the vertical to interpolate data on isobaric
surfaces to constant height surfaces if you need very accurate
estimates.  Look for zinterp.gs. It might even be in the grads
scripting library on the web site.  I use that script to display 0-6
km shear on my forecasting web site.  Here is an example:
http://www.meteor.iastate.edu/~jdduda/forecast/NAM/18Z/0-6_shear_f24.gif

Jeff Duda

On Sun, Sep 1, 2013 at 6:12 PM, Nimrod Micael <nmicael at aggies.ncat.edu> wrote:
> @Jeff,
>
> I see but is it approximation? That's my understanding from Rich Thompson's
> post. http://www.stormtrack.org/forum/archive/index.php/t-23323.html
>
>
> On Sun, Sep 1, 2013 at 6:55 PM, Jeff Duda <jeffduda319 at gmail.com> wrote:
>>
>> The contours are just the magnitude of the shear vector, but that's
>> not the same as the difference in wind speed at two levels.
>>
>> On Sun, Sep 1, 2013 at 4:58 PM, Nimrod Micael <nmicael at aggies.ncat.edu>
>> wrote:
>> > I see what your saying Jeff. But what if you are interested in the
>> > magnitude
>> > only of u and v and not the two separate u and v vectors. I am trying to
>> > get
>> > a map like this....
>> >
>> > http://www4.ncsu.edu/~nwsfo/storage/cases/20100425/shr6_10042600.gif
>> >
>> > This doesnt have two separate vectors: u and v.
>> >
>> >
>> >
>> >
>> >
>> > On Sun, Sep 1, 2013 at 5:52 PM, Jeff Duda <jeffduda319 at gmail.com> wrote:
>> >>
>> >> The way you're doing it, you're only computing the difference in wind
>> >> speed between two layers.  If you're trying to calculate vertical wind
>> >> shear, you should be calculating the vector difference, which is the
>> >> difference in the components.  So you should have a delta-U wind
>> >> component of the shear (u500-usfc) and a delta-V component of the
>> >> shear (v500-vsfc).  Those are the two quantities you would display to
>> >> get the vectors.
>> >>
>> >> Jeff
>> >>
>> >> On Sun, Sep 1, 2013 at 3:39 PM, Nimrod Micael <nmicael at aggies.ncat.edu>
>> >> wrote:
>> >> > I see Jeff. So then how would i make it to display the magnitude of
>> >> > u,v
>> >> > for
>> >> > 2 different levels then? Since I am taking the difference between the
>> >> > 500 mb
>> >> > wind and the sfc wind?
>> >> >
>> >> >
>> >> >
>> >> > On Sun, Sep 1, 2013 at 4:33 PM, Jeff Duda <jeffduda319 at gmail.com>
>> >> > wrote:
>> >> >>
>> >> >> displaying wind barbs requires two inputs in the display command
>> >> >> (i.e., 'd u;v').  You are only supplying one.
>> >> >>
>> >> >> Jeff Duda
>> >> >>
>> >> >> On Sun, Sep 1, 2013 at 2:53 PM, Nimrod Micael
>> >> >> <nmicael at aggies.ncat.edu>
>> >> >> wrote:
>> >> >> > The shaded is plotting fine but the wind barb is not showing up.
>> >> >> > Can
>> >> >> > anyone
>> >> >> > help me out why?
>> >> >> >
>> >> >> > 'set gxout shaded'
>> >> >> > 'set lev 1000'
>> >> >> > 's= mag(u,v)'
>> >> >> > 'set lev 500'
>> >> >> > 'a = mag (u,v)'
>> >> >> > 'set cmin 20'
>> >> >> > 'bulk = (a-s)*1.92'
>> >> >> > 'd bulk'
>> >> >> >
>> >> >> > 'set gxout barb'
>> >> >> > 'set lev 1000'
>> >> >> > 'barbs= mag(u,v)'
>> >> >> > 'set lev 500'
>> >> >> > 'barba = mag (u,v)'
>> >> >> > 'set cmin 20'
>> >> >> > 'bulkb = (barba-barbs)*1.92'
>> >> >> > 'd bulkb'
>> >> >> >
>> >> >> >
>> >> >> > Wind vectors are not showing up. Why???
>> >> >> >
>> >> >> > Thanks.
>> >> >> >
>> >> >> > --
>> >> >> > Nimrod Micael
>> >> >> >
>> >> >> > _______________________________________________
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>> >> >> > gradsusr at gradsusr.org
>> >> >> > http://gradsusr.org/mailman/listinfo/gradsusr
>> >> >> >
>> >> >>
>> >> >>
>> >> >>
>> >> >> --
>> >> >> Jeff Duda
>> >> >> Graduate research assistant
>> >> >> University of Oklahoma School of Meteorology
>> >> >> Center for Analysis and Prediction of Storms
>> >> >> _______________________________________________
>> >> >> gradsusr mailing list
>> >> >> gradsusr at gradsusr.org
>> >> >> http://gradsusr.org/mailman/listinfo/gradsusr
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > --
>> >> > Nimrod Micael
>> >> >
>> >> > _______________________________________________
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>> >> > gradsusr at gradsusr.org
>> >> > http://gradsusr.org/mailman/listinfo/gradsusr
>> >> >
>> >>
>> >>
>> >>
>> >> --
>> >> Jeff Duda
>> >> Graduate research assistant
>> >> University of Oklahoma School of Meteorology
>> >> Center for Analysis and Prediction of Storms
>> >> _______________________________________________
>> >> gradsusr mailing list
>> >> gradsusr at gradsusr.org
>> >> http://gradsusr.org/mailman/listinfo/gradsusr
>> >
>> >
>> >
>> >
>> > --
>> > Nimrod Micael
>> >
>> > _______________________________________________
>> > gradsusr mailing list
>> > gradsusr at gradsusr.org
>> > http://gradsusr.org/mailman/listinfo/gradsusr
>> >
>>
>>
>>
>> --
>> Jeff Duda
>> Graduate research assistant
>> University of Oklahoma School of Meteorology
>> Center for Analysis and Prediction of Storms
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>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>
>
>
>
> --
> Nimrod Micael
>
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>



-- 
Jeff Duda
Graduate research assistant
University of Oklahoma School of Meteorology
Center for Analysis and Prediction of Storms