;***********************
; h_lat_4.ncl
;***********************
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
 fili  = "mxclim.nc"                              ; filename
 
 f     = addfile (fili , "r")                     ; add file
 u     = f->U(0,:,:)                              ; get u for January
 
 wks   = gsn_open_wks ("ps", "h_lat" )           ; open workstation
; ===========================
; Modifies default plot by 
; shading values less than zero
; ===========================
 res=True                                         ; plot mods desired
 res@gsnDraw         = False                      ; do not draw  
 res@gsnFrame        = False                      ; do not advance frame
 res@cnLevelSpacingF = 5.0                        ; choose contour spacing

; note u is already on pressure levels. If this were model data, it
; would be necessary to interpolate from the hybrid coordinates to 
; pressure levels.

 plot  = gsn_csm_pres_hgt(wks, u, res )   
 plot  = ShadeLtContour (plot, 0., 3)
 draw(plot)
 frame (wks)
end