plotting wind between two values

Hello
I am trying to plot wind between two values using the resources
vcres@vcLevelSelectionMode ="ManualLevels"
vcres@vcMinLevelValF = 0
vcres@vcMaxLevelValF =5
but it doesnot work
any suggestion?
the script , I download it from the NCL website and i just add the previous
three line to it .
----------------------------------------------------------------------

; vector_3.ncl
;
; Concepts illustrated:
; - Drawing a black-and-white vector plot over a cylindrical equidistant
map
; - Adding a time stamp to a plot
; - Thinning vectors using a minimum distance resource
; - Moving the vector reference annotation to the top right of the plot
;----------------------------------------------------------------------
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"
;************************************************
begin
;************************************************
; read in netCDF file
;************************************************
  a = addfile("uv300.nc","r")
;************************************************
; read in zonal [u] and meridional [v] winds (July)
;************************************************
  u = a->U(1,:,:)
  v = a->V(1,:,:)
;************************************************
; create plot
;************************************************
  wks = gsn_open_wks("x11","vector") ; open a ps file

  vcres = True ; plot mods desired
  vcres@gsnFrame = False ; so we can draw time
stamp
  vcres@vcRefAnnoOrthogonalPosF = -1.0 ; move ref vector up
  vcres@vcRefMagnitudeF = 10.0 ; define vector ref mag
  vcres@vcRefLengthF = 0.045 ; define length of vec
ref
  vcres@vcGlyphStyle = "CurlyVector" ; turn on curly vectors
  vcres@vcMinDistanceF = 0.017

vcres@vcLevelSelectionMode ="ManualLevels"
vcres@vcMinLevelValF = 0 ; m/s
vcres@vcMaxLevelValF =5; m/s

  vector = gsn_csm_vector_map_ce(wks,u,v,vcres)
;************************************************
; add time stamp to plot
;************************************************
  infoTimeStamp(wks,0.025,"uv300.nc") ; arguments are workstation
                                           ; size of text desired, and
                                           ; right string.
  frame (wks)
end

thanks in advance

-- 
===============
Ahmed Lasheen
Junior researcher at Cairo Numerical Weather Prediction Center (CNWPC)
Egyptian Meteorological Authority(EMA)
Cairo,Egypt
===============

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Received on Wed Apr 18 10:13:50 2012