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

begin
  a = addfile("T.nc","r")

  T = a->T
  print(T&lev)    ; Notice the values are irregularly-spaced.

  wks = gsn_open_wks("ps","irregular1b")

;
; The Y axis will be irregularly-spaced. This is because NCL will
; regularly-space the T&lev values on the Y axis, regardless if the
; values themselves are regularly spaced.
;
  res             = True
  res@gsnMaximize = True                ; Maximize plot in frame.

  res@tiMainString = "Y axis values irregularly spaced"

;
; Use some tickmark resources to label the Y axis with the exact 
; same values in our "T&lev" array. This way, you can see how the
; values are spaced.
;
  res@tmYLMode = "Explicit"
  res@tmYLValues = T&lev
  res@tmYLLabels = T&lev
  plot = gsn_csm_contour(wks,T,res)
end