Re: Units used for drawing windbarbs

Hi TJ,
According to the documentation:
"If the velocity is less than 2.5 in magnitude, a circle is drawn
instead of the barbed shaft. Otherwise half ticks represent 5 units of
magnitude, full ticks represent 10 units, and pennants represent 50
units. By convention, the units usually represent knots. The pennants
are drawn using a filled polygon, while the ticks, the shaft, and the
calm circle are all rendered with polylines. Unlike the other glyph
styles, wind barbs maintain a basically uniform length for all magnitudes."

http://www.ncl.ucar.edu/Document/Graphics/Resources/vc.shtml#vcGlyphStyle

What that says to me is that you don't need to convert your units from
m/s to knots if you don't want to. If you input an array into the
plotting function with units of m/s, then the wind barb color will be
dependent on m/s. (NCL will not convert it to knots.)
Adam

TJ wrote:
> Hi,
> I am using gsn_vector(wks,ugrid,vgrid,res) with
> uv_res_at_vcGlyphStyle = "WindBarb" to create wind profiles over time.
> ugrid and vgrid are in m/s.
>
> Are the wind barbs drawn still following the knots conventions as to number and
> type of feathers, or do I need to change the units before drawing the plot?
> I am using uv_res_at_vcMonoWindBarbColor = False so the barbs are colored.
> Will their color be dependent on knots or m/s?
>
> TJ Olney
>
> Var summaries:
> Variable: ugrid
> Type: float
> Total Size: 1344 bytes
> 336 values
> Number of Dimensions: 2
> Dimensions and sizes: [bottom_top | 21] x [Time | 16]
> Coordinates:
> Number Of Attributes: 6
> coordinates : XLONG XLAT
> stagger :
> units : m s-1
> description : x-wind component
> MemoryOrder : XYZ
> FieldType : 104
>
>
> Variable: vgrid
> Type: float
> Total Size: 1344 bytes
> 336 values
> Number of Dimensions: 2
> Dimensions and sizes: [bottom_top | 21] x [Time | 16]
> Coordinates:
> Number Of Attributes: 6
> coordinates : XLONG XLAT
> stagger :
> units : m s-1
> description : y-wind component
> MemoryOrder : XYZ
> FieldType : 104
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-- 
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Adam Phillips			             asphilli_at_ucar.edu
National Center for Atmospheric Research   tel: (303) 497-1726
ESSL/CGD/CAS                               fax: (303) 497-1333
P.O. Box 3000				
Boulder, CO 80307-3000	  http://www.cgd.ucar.edu/cas/asphilli
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