;this is an example

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/wrf/WRF_contributed.ncl"

begin

;READ IN WRFOUT FILE

  date="08-10_00"
  direc1="/nfs/vapor3/local/vol01/scratch/binzhang/wrfout/200608_standard_bc/"
  fn1=addfile(direc1+"wrfout_d01_2006-"+date+":00:00.nc","r") ;filename
  
  direc2="/nfs/vapor3/local/vol01/scratch/binzhang/wrfout/200608_nobc/"
  fn2=addfile(direc2+"wrfout_d01_2006-"+date+":00:00.nc","r")

;EXTRACT FILED TO BE PLOTTED 

 u1 = fn1->U
 v1 = fn1->V
 u2 = fn2->U
 v2 = fn2->V

;extract the lowest level 
   u1l = u1(:,0,:,:)
   v1l = v1(:,0,:,:)
   u2l = u2(:,0,:,:)
   v2l = v2(:,0,:,:)
  
  w1=u1l
  w2=u1l

  do i=0,71
    do j=0,75
      do k=0,99
        ; aa=(u1l(i,j,k)^2) + (v1l(i,j,k)^2)
        ; bb=(u2l(i,j,k)^2) + (v2l(i,j,k)^2)
          w1(i,j,k) = sqrt((u1l(i,j,k)*u1l(i,j,k))+(v1l(i,j,k)*v1l(i,j,k)))
          w2(i,j,k) = sqrt((u2l(i,j,k)*u2l(i,j,k))+(v2l(i,j,k)*v2l(i,j,k)))
          w = w1-w2
      end do
    end do
  end do
  
  wtvg = dim_avg_n(w,0) ;time averaging data
   
   wtvg@units="m/s"

;  print(max(wtvg))
;  print(min(wtvg))

;=======================================================================
;SET UP PLOTTING PARAMETERS

;creating workstations to plot to different file
  off = "pdf"      ; output file form
  ofn = "com_windspeed"     ; output file name
  wks=gsn_open_wks(off,ofn+"_"+date)
  gsn_define_colormap(wks,"WhViBlGrYeOrRe")     ;choose colormap for wks

;assign plotting resources
  res = True
  res@gsnMaximize = True
  res@gsnSpreadColors = True   ;use full range of color map
  res@cnFillOn = True          ;turn on color fill
  res@cnLinesOn = False        ;turn off contour lines
  res@cnLevelSelectionMode = "ManualLevels"  ;set explicit contour levels
  res@cnMinLevelValF = -12
  res@cnMaxLevelValF = 12
  res@cnLevelSpacingF = 2

  res@tiMainString = "Surface_windspeed__SS-NS"+date+"UTC"
  
  res@mpDataBaseVersion = "Ncarg4_1"
  res@mpOutlineOn = True 
  res@mpOutlineSpecifiers=(/"China:states","Taiwan"/)
  res@mpOutlineBoundarySets = "GeophysicalAndUSStates";"Geophysical" "AllBoundaries" "National"
  res@mpGridLineColor             = "Black"   
  res@mpLimbLineColor             = "Black"   
  res@mpNationalLineColor         = "Black"   
  res@mpPerimLineColor            = "Black" 
 
;=======================================================================
;Use WRF_contributed PROCEDURE TO SET MAP RESOURCES
  WRF_map_c(fn1,res,0) 



;define lat,lon

  wtvg@lat2d = fn1 ->XLAT(0,:,:)
  wtvg@lon2d = fn1 ->XLONG(0,:,:)

;plot bc at the lowest level
  ;plot = gsn_csm_contour_map(wks,wtvg,res)
  plotpdf = gsn_csm_contour_map(wks,wtvg,res)


end