;----------------------------------------------------------------------
; This is a basic NCL template for drawing vectors over a map.
;
; Use "vector_template.ncl" if you don't need to put the
; vectors over a map.
;----------------------------------------------------------------------
; Note: as of NCL V6.2.0, you don't need these load commands
;----------------------------------------------------------------------
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"

begin
;---Read data
  filename = "file.nc"
  a = addfile(filename,"r")
  u = a->u
  v = a->v 

  lat = a->lat      ; Only necessary if "u" and "v" don't 
  lon = a->lon      ; contain 1D coordinate arrays.

;---Open workstation
  wks = gsn_open_wks("x11","vector_map")   ; "ps", "pdf", "png"

;---Set some resources
  res                      = True

  res@gsnMaximize          = True     ; maximize plot in frame

;---Set these two if arrows are too short
  res@vcRefLengthF         = some floating point value
  res@vcRefMagnitudeF      = some floating point value

  res@vcMinFracLengthF     = 0.05     ; length of min vector as fraction
                                      ; of reference vector.

  res@vcMinDistanceF       = 0.02     ; "thin" vectors

  res@vcMonoLineArrowColor = False    ; color arrows based on magnitude
  res@vcLevelPalette       = "rainbow"         ; define colormap for vectors

  res@vcGlyphStyle         = "CurlyVector"     ; turn on curly vectors

  res@tiMainString         = "Data file is " + filename

;---Set to False if regional data or setting vfXArray/vfYArray
  res@gsnAddCyclic      = True

  res@vfXArray          = lon   ; Only necessary if u and v don't
  res@vfYArray          = lat   ; contain 1D coordinate arrays

;
; Zoom in on map if desired. There are other ways to zoom in on
; map if you have a different projection, like lambert conformal.
;
  res@mpMinLatF         = min(lat)
  res@mpMaxLatF         = max(lat)
  res@mpMinLonF         = min(lon)
  res@mpMaxLonF         = max(lon)
  res@mpCenterLonF      = (res@mpMinLonF + res@mpMaxLonF) / 2.

  vector = gsn_csm_vector_map(wks,u,v,res)
end