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wrf_vector

Creates a vector plot from ARW WRF model output.

Prototype

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

	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 "PlotLeveID" attribute of the data_u variable will be used, if available.

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

Other vector resources are internally set by this routine:

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

WRF-related questions should be sent to wrfhelp@ucar.edu.

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://www.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/