;========
;NCL tips
;========

;------------
; color table
;------------

  gsn_define_colormap(wks,"nrl_sirkes")	; define color table
  gsn_reverse_colormap(wks)		; reverse color order
  colors = gsn_retrieve_colormap(wks)	; retrieve color table to modify
  colors(11,:) = (/1.0,1.0,1.0/)	; modify color table to white
  colors(12,:) = (/0.9,0.9,0.9/)	; modify color table to gray
  colors(13,:) = (/1.0,1.0,1.0/)	; modify color table to white
  gsn_define_colormap(wks,colors)	; re-defince new color table

;-----------
; color fill
;-----------

  res@cnFillOn = True			; color fill
  res@cnFillMode = "CellFill"		; fill each grid cell without smoothing

; color label
  res@lbLabelBarOn  = Ture		; colar bar "on" or "off"
  res@lbOrientation = "vertical"	; "vertical" or "horizontal"
  res@lbBoxMinorExtentF = 0.2		; slim width
  res@lbLabelStride = 2			; label interval
  res@gsnSpreadColors     = True	; spread out color table
  res@gsnSpreadColorStart = 2		; starting color
  res@gsnSpreadColorEnd   = 20		; ending color

;--------------
; line contours
;--------------

  res@cnLinesOn = True			; contour lines
  res@cnInfoLabelOn = False		; contour info label
  res@cnLineThicknessF = 2		; line thickness
  res@gsnContourZeroLineThicknessF = 2	; doubles thickness of zero contour
  res@gsnContourZeroLineThicknessF = 0	; omit zero contour
  res@gsnContourNegLineDashPattern = 1	; sets negative contours to dash pattern 1

;---------------
; contour labels
;---------------

  res@cnLineLabelsOn = False		; contour line labels "on" of "off"
  res@cnLineLabelBackgroundColor = "white"  ; label background color
  res@cnLineLabelInterval  = 2		; label interval
  res@cnLineLabelFontHeightF = 0.015	; change label font size

;-------------------------
; to define contour levels
;-------------------------

; Manual setting
  res@cnLevelSelectionMode = "ManualLevels"  ; set manual contour levels
  res@cnMinLevelValF       = -6.             ; set min contour level
  res@cnMaxLevelValF       =  6.             ; set max contour level
  res@cnLevelSpacingF      =  2.             ; set contour spacing

; Explicit setting
  res@cnLevelSelectionMode = "ExplicitLevels"   ; set explicit contour levels
  res@cnLevels             = (/ 0.5, 1.0, 2.0 \ ; set unequal contour levels
                              , 3.0, 4.0, 5.0 \
                              , 7.5,10.0 /)

;-------
; vector
;-------

  res@vcRefMagnitudeF           = 4.0             ; define vector ref mag
  res@vcRefLengthF              = 0.045           ; define length of vec ref
  res@vcRefAnnoOrthogonalPosF   = -1.0            ; move ref vector
  res@vcRefAnnoArrowLineColor   = "black"         ; change ref vector color
  res@vcRefAnnoArrowUseVecColor = False           ; don't use vec color for ref

  res@vcGlyphStyle            = "CurlyVector"     ; turn on curley vectors
  res@vcLineArrowColor        = "white"           ; change vector color
  res@vcLineArrowThicknessF   = 2.0               ; change vector thickness
  res@vcVectorDrawOrder       = "PostDraw"        ; draw vectors last

;-------
; resize
;-------

  mpShapeMode = "FreeAspect"  ; necessary for maps

; pressure-latitude
  vpWidthF = 0.7
  vpHeightF = 0.5

; N. America
  vpWidthF = 0.5
  vpHeightF = 0.5

;----------------
; to set a region
;----------------

  res@gsnAddCyclic = True	; add cyclic point
  res@mpMinLonF =   0.
  res@mpMaxLonF = 360.
  res@mpMinLatF = -40. 
  res@mpMaxLatF =  40.
  res@mpFillOn  = False		; color fill continents
  res@mpCenterLonF = 180	; specify center longitude
  res@gsnMajorLonSpacing = 60
  res@gsnMinorLonSpacing = 10
  res@gsnMajorLatSpacing = 30
  res@gsnMinorLatSpacing = 10

;-----------------
; to change titles
;-----------------

  res@tiMainString = ""      ; main title
  res@gsnLeftString   = ""   ; left subtitle (variable name)
  res@gsnRightString  = ""   ; center subtitle
  res@gsnCenterString = ""   ; right subtitle (unit)
  res@tiXAxisString   = ""   ; title for horizontal axis  
  res@tiYAxisString   = ""   ; title for vertical axis

;-------------------
; to change fontsize
;-------------------

; fontsize of the main title
  res@tiMainFontHeightF = 0.022

; fontsize of the subtitles
  res@txFontHeightF = 0.02

; fontsize of X & Y axes
  res@tiXAxisFontHeightF = 0.02
  res@tiYAxisFontHeightF = 0.02

; fontsize of tickmark labels
  res@tmXBLabelFontHeightF = 0.02
  res@tmYLLabelFontHeightF = 0.02

;---------------------
; types of vector plot
;---------------------

  plot = gsn_csm_vector_map_ce            ; vector plot over a map
  plot = gsn_csm_vector_map_polar         ; vector plot over a ploar stereographic map
  plot = gsn_csm_vector_scalar_map_ce     ; vector plot over a scalar contour plot
  plot = gsn_csm_vector_scalar_map_polar  ; vector plot over a scalar contour plot
                                          ; over a polar stereographic map
  plot = gsn_csm_pres_hgt_vector          ; vector plot over pressure/height countour plot

; adjust Y-axis
  res@tmYLAutoPrecision = False
  res@tmYLPrecision = 1                ; one digit (e.g., 1.0 -> 1)
  res@gsnYAxisIrregular2Linear = True  ; constant spacing
  res@trYReverse = True                ; reverse axis

;-------------------
; add contours to plot
;-------------------

  delete(res)
  res                 = True
  res@gsnDraw         = False
  res@gsnFrame        = False
  cplot = gsn_csm_contour(wks,speed,res)
  overlay(plot,cplot)
  draw(plot)
  frame(wks)

;--------------------
; add markers to plot
;--------------------

  x = 1.0
  y = 2.0

  pmres               = True
  pmres@gsMarkerColor = "red"
  pmres@gsMarkerIndex = 16
  pmres@gsMarkerSizeF = 0.01
  dum = gsn_add_polymarker(wks,plot,x,y,pmres)

;------------
; annual mean
;------------

; 12 month data to annual mean data
  yyyymm = yyyymm_time(1850,1850,"integer")
  tmp_ann = month_to_annual_weighted(yyyymm,tmp,1)
  var = tmp_ann(0,:,:,:)