[gradsusr] Question about why the wind vectors barbs not showing up for the 0-6 KM Shear difference
Nimrod Micael
nmicael at aggies.ncat.edu
Sun Sep 1 19:58:35 EDT 2013
Yes that's exactly what I want...what you have in your example on your
site. I understand that I have to do this:
***although height is in km though in my script**
"define mag1000="zinterp(mag(u,v),height,1000)
"define mag6000="zinterp(mag(u,v),height,6000)
"06shear = mag6000-mag1000?
"d 06shear"
Would I then be able to do just do that?
function zinterp(field,zgrid,zlev)
*----------------------------------------------------------------------
*
* Bob Hart (hart at ems.psu.edu) / PSU Meteorology
* 3/4/1999
*
* GrADS function to interpolate within a 3-D grid to a specified
* height level. Can also be used on non-pressure level data, such
* as sigma or eta-coordinate output where height is a function
* of time and grid level.
*
* Advantages: Easy to use, no UDFs. Disadvantages: Can take 3-10 secs.
*
* Arguments:
* field = name of 3-D grid to interpolate
*
* zgrid = name of 3-D grid holding height values at each gridpoint
* Units of measurement are arbitrary.
*
* zlev = height level at which to interpolate (having same units as zgrid)
*
* Function returns: defined grid interp holding interpolated values
*
* NOTE: Areas having zlev below bottom level or above upper level
* in output will be undefined.
*
* NOTE: No distinction in the function is made between height above
* sea level, height above ground surface, or geopotential. The
* function will give output regardless of which is sent.
* It is up to the user to be aware which height variable is
* being passed to the function and treat the output accordingly.
*
* Example function calls:
*
* "d "zinterp(temp,height,5000)
*
* Would display a temperature field interpolated to 5000.
*
* "define t1000="zinterp(temp,height,1000)
*
* Would define a new variable, t1000, as a temp field at 1000.
*
* "d p1000="zinterp(lev,height,1000)
*
* Would display a field of the pressure at a height of 1000.
*
On Sun, Sep 1, 2013 at 7:30 PM, Jeff Duda <jeffduda319 at gmail.com> wrote:
> 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
> >> >> >> >
> >> >> >> > _______________________________________________
> >> >> >> > 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
> >> >> >> _______________________________________________
> >> >> >> 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
> >> >> _______________________________________________
> >> >> 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
> >> _______________________________________________
> >> 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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>
--
Nimrod Micael
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