FNL数据中，包含了Ice Cover数据，在北极地区就是Sea ICE。
用wgrib2将FNL原始的grib2格式转换成netcdf格式:
wgrib2 gdas1.fnl0p25.2016072400.f00.grib2 -netcdf gdas1.fnl0p25.2016072400.f00.nc
然后用NCL绘图如下，发脚本纪念。
load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/cd_string.ncl"
;************************************************
begin
;************************************************
; read in atmospheric data
;************************************************
a = addfile("gdas1.fnl0p25.2016072400.f00.nc","r")
icec = a->ICEC_surface(0,:,:)
;------for time------------------
times = a->time
times2 = times
times2 = times + todouble(3600*8) ; time to BJT
format = "%Y-%N-%D_%H:%M"
stime = cd_string(times2 , format) ;simulation time
;************************************************
; create plot
;************************************************
wks = gsn_open_wks("png","polar_icec_ste") ; send graphics to PNG file
;gsn_define_colormap(wks, "wgne15")
cmap = RGBtoCmap("./Color_seaice.rgb")
res = True
res@gsnMaximize = True
res@gsnDraw = False
res@gsnFrame = False
res@mpProjection = "Stereographic"
res@mpCenterLatF = 90 ; Centered over north pole
res@mpCenterLonF = 90 ; Centered over north pole
res@mpLimitMode = "LatLon"
res@mpMinLatF = 60.0
res@pmTickMarkDisplayMode = "Always" ; Nicer tickmark labels
res@mpGridAndLimbOn = True ; Turn on lat/lon grid
;res@gsnMajorLatSpacing = 10. ;---doesn't work---
;res@mpGridSpacingF = 10.
res@mpGridLonSpacingF = 15.0
res@mpGridLatSpacingF = 10.0
res@mpGridLineDashPattern = 2 ; Dashed lines
res@mpFillOn = True;False
res@mpLandFillColor = "grey";"transparent" ; fill land with "dafult"
res@mpFillDrawOrder = "PostDraw"
res@cnFillOn = True ; color fill
res@cnLinesOn = False ; no contour lines
res@cnFillColors = cmap
res@cnLevelSelectionMode = "ExplicitLevels"
res@cnLevels = fspan(0.15,0.95,17)
res@lbLabelStride = 3 ;
res@tiMainString = stime+" (BJT)"
plot = gsn_csm_contour_map(wks,icec({50.:90.},:),res) ; Create plot
;---Create lat/lon arrays for location of latitude labels.
lats = ispan(60,90,10)
nlat = dimsizes(lats)
lons = new(nlat,integer)
lons = res@mpCenterLonF;90 ;
;---Resources for text strings
txres = True
txres@txFontHeightF = 0.015
dum = gsn_add_text(wks,plot,""+lats+"~F34~0~F~N",lons,lats,txres)
;---Drawing the plot will draw the attached latitude labels
draw(plot)
frame(wks)
end
