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20011218: Computing wind shear

Matt,

The station elevation can be obtained with the STNDEX parameter "SELV".
SELV is also output in the station information at the top of the output
along with station lat/lon and time.

The surface should be the first level of the sounding output. The hght of that
levels will be the height of the station.

The SHRM parameter will be the value in each layer of the sounding. That is,
the value is calculated using each successive level of the sounding. To
only get the the 1091km level, you would use: levels = 1091. However, the
value of SHRM that would be output would be the shear in the layer in which
the 1091 meter level occurs. It would not be the mean from surface to that 
layer.
There is no function that would give you the mean of shear in a specified 
layer.  
The STNDEX functions allow the user to specify the layer depth and surface using
the "!" characters. However, SHRM is a level parameter, not a STNDEX function.

Steve Chiswell
Unidata User Support





>From: "Matthew Menne" <address@hidden>
>Organization: National Climatic Data Center, NOAA
>Keywords: 200112181525.fBIFPsN07532

>This is a multi-part message in MIME format.
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>I would like to calculate the wind shear magnitude between the surface
>and a specified height above ground level (AGL) and I'm not sure that I
>am doing it correctly (using SNLIST).
>
>Is there a way to specify height AGL directly or do I need to know the
>station's elevation and then add some height value to it?
>
>I tried the latter in an attempt to get the mean wind shear for the
>layer 0-1km AGL for JAN (wmo=72235) whose elevation is 91 meters
>
>
>   snlist << EOF
>      snfile = ${file}_upa.gem
>      dattim = all
>      output = f/shear_${STN}_19${YEAR}${mon_str}
>      snparm = SHRM
>      stndex =
>      levels = 91-1091-1000
>      vcoord = hght
>      mrgdat = y
>      area = @${STN}
>      r
>
>
>When I run a script like the one above I get two numbers: one for 91 m
>and another for 1091 m, but I only expected one number (the mean between
>91 and 1091 m).  Could you help me interpret these numbers or suggest
>how to extract the shear values that I'm looking for?  Also, is there
>any way to obtain and use the station elevation value automatically in a
>script somehow?
>
>Thanks for the help.
>
>
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>n:Menne;Matthew
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