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wrf_vector

Creates a vector plot from ARW WRF model output.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"      ; These two libraries are automatically
load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"    ; loaded from NCL V6.4.0 onward.
                                                              ; No need for user to explicitly load.

	function wrf_vector (
		nc_file       : file,     
		wks           : graphic,  
		data_u [*][*] : numeric,  
		data_v [*][*] : numeric,  
		res           : logical   
	)

	return_val [1] :  graphic

Arguments

nc_file

Reference to an input netCDF file opened with addfile.

wks

An NCL Workstation identifier. The identifier is one returned either from calling gsn_open_wks or calling create to create a Workstation object.

data_u

A two-dimensional array of the U component of the wind.

data_v

A two-dimensional array of the V component of the wind.

res

A variable containing an optional list of plot resources, attached as attributes.

Return value

A scalar id of the plot created is returned.

Description

This function creates a vector plot (but does not draw it). To draw the plot, see the example below.

If data has a _FillValue attribute, this value will be used as a missing value.

If data_u has a "description" attribute, this value will be used in the plot title. (See description of "FieldTitle" attribute below.)

This function recognizes some special resources that can be attached as attributes to res:

• NumVectors - this defaults to 25. If this resource is set along with vpWidthF, then these two values will be used to determine values for vcMinDistanceF and vcRefLengthF (opts@vpWidthF/opts@NumVectors). Otherwise, these two resources will default to 0.02.

• FieldTitle - This becomes the main title of the vector plot. If not set, then the "description" attribute of the data_u variable will be used, if available.

• SubFieldTitle - if set, this will be appended to the FieldTitle title with a space between the two.

• UnitLabel - if set, this will be appended to the existing FieldTitle title in parentheses. If not set, the "units" attribute of the data_u variable will be used, if available.

• PlotLevelID - if set, this will be appended to the existing FieldTitle title with an " at " between the two. If not set, the "PlotLevelID" attribute of the data_u variable will be used, if available.

• NoHeaderFooter - Turn off all the extra titles. This is useful if you need to panel the plot later.

The final main title could look something like "FieldTitle SubFieldTitle (UnitLabel) at PlotLevelID".

Other vector resources are internally set by this routine:

• vcGlyphStyle - "WindBarb"
• vcWindBarbColor - "black"
• vcRefAnnoOn - False (default is normally True)
• vcMinFracLengthF - 2.0

wrf_vector is part of a library of functions and procedures in WRFUserARW.ncl written to help users plot ARW WRF model data.

See Also

wrf_contour, wrf_map_overlays, wrf_overlays, wrf_map

Examples

Example 1

  load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
  load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"

  a = addfile("wrfout_d01_2000-01-24_12:00:00.nc","r")

  wks = gsn_open_wks("x11","test")

  u10 = wrf_user_getvar(a,"U10",0)   ; U component of the wind at 10m
  v10 = wrf_user_getvar(a,"V10",0)   ; V component of the wind at 10m

  res = True
  res@gsnDraw  = True    ; Forces the plot to be drawn
  res@gsnFrame = True    ; Frame advance
  vector = wrf_vector(a,wks,u10,v10,res)

You can see some other example scripts and their resultant images at:

http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/

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