[ncl-talk] Plotting over the ocean

[Grace Choi]

Thank you Rashed and Rick for your helpful feedback!

Sincerely,
Grace

On Thu, Feb 8, 2018 at 5:18 PM, Rick Brownrigg <brownrig at ucar.edu> wrote:

> (sorry -- I meant to post this to the whole group):
>
> Hi Grace,
>
> The dataset has no valid data over the oceans, which is why it is not
> plotted. There are many NaNs in it, which the script is converting to
> missing_values. If you instead set those NaNs to something that looks like
> real data, you'll see that they occur precisely over the ocean
>
> Hope that helps...
> Rick
>
>
> On Thu, Feb 8, 2018 at 2:00 PM, Grace Choi <gracesh27 at gmail.com> wrote:
>
>> Hello,
>>
>> I have been trying to find and apply a function that allows me to plot
>> over the ocean as well as the land, but I have not been able to succeed.
>>
>> If someone could direct me to a reference where mapping over the ocean is
>> talked about, or help me with the script itself, I would really appreciate
>> it.
>>
>> I am attaching the script and the netCDF file I am working with here for
>> reference:
>>
>> begin
>>
>>
>> ;************************************************************
>>
>> ; START user input
>>
>> ;************************************************************
>>
>>
>> datadir = "./"
>>
>> filename = "Dalhousie_PM2.5_2011.nc"
>>
>>
>> ; specify latitude and longitude bounds for plot:
>>
>> ; latitude spans -54.75 degrees to 69.75 degrees
>>
>> minlat = 25
>>
>> maxlat = 50
>>
>>
>> ; longitude spans -179.95 to 179.95 degrees
>>
>> minlon = -130
>>
>> maxlon = -70
>>
>>
>> title_string = "Dalhousie PM2.5 2011" ; whatever you want the title on
>> the plot to be
>>
>>
>> plot_name = "dalhousie_ocean_PM25_2011"   ; what you want the plot file
>> name to be (less the extension/format)
>>
>> plotfiletype = "pdf" ; check NCL documentation for other plot output file
>> formats
>>
>>                      ; options include "pdf" and "png"
>>
>>
>> showgrid = "yes"     ; options are "yes" (plot will show grid size and
>> look blocky)
>>
>>                      ; or "no" (plot will show smoothed-out data)
>>
>>
>> ;************************************************************
>>
>> ; read in the file:
>>
>> ;************************************************************
>>
>>
>> fin = addfile(datadir+filename,"r")
>>
>> ; now read in the variables. I found the variable names using the
>> following lines:
>>
>> ; varnames = getfilevarnames(fin)
>>
>> ; print(varnames)
>>
>> ; then used the resulting names below:
>>
>> lats = fin->LAT
>>
>> lons = fin->LON
>>
>> PM25data = fin->PM25
>>
>>
>> printVarSummary(PM25data) ; will tell us the shape of the PM2.5 array
>>
>> ; that tells us it's arranged (lat,lon) and has units of ug/m3
>>
>> ; you can comment out that line, if you want!
>>
>>
>> ; this dataset has IEEE NaN "values," which NCL doesn't like.
>>
>> ;print(num(isnan_ieee(PM25data)))
>>
>> ; so let's replace them with something NCL can handle better:
>>
>> if (any(isnan_ieee(PM25data))) then
>>
>>    value = -999.
>>
>>    replace_ieeenan(PM25data,value,0)
>>
>>    PM25data at _FillValue = value
>>
>> end if
>>
>>
>> ; this will print out the min and max of the -whole- dataset (not just
>> the part you sample)
>>
>> ; which can be helpful for picking out contour levels (res at cnLevels,
>> below)
>>
>> printVarSummary(PM25data)
>>
>> printMinMax(PM25data,True)
>>
>> ;**********************************************************************
>>
>> ; plot section
>>
>> ;**********************************************************************
>>
>> res = True
>>
>>
>> res at tiMainString = "Dalhousie PM2.5 2011"
>>
>> name = plot_name
>>
>> print("Dalhousie PM2.5 2011 "+name)
>>
>> wks   = gsn_open_wks("pdf", name)
>>
>>
>> res at cnLevelSelectionMode = "ExplicitLevels"  ; Set contour levels
>> manually
>>
>> res at cnFillOn             = True                ; turn on color
>>
>> if (showgrid.eq."yes") then
>>
>>    res at cnFillMode           = "CellFill"
>>
>> end if
>>
>> res at gsnSpreadColors      = True                ; use full colormap
>>
>> res at cnLinesOn            = False               ; turn off contour lines
>>
>>
>> ; specify color table you want:
>>
>> gsn_define_colormap(wks,"sunshine_9lev")
>>
>>
>> ; specify which values bound color changes in the plot:
>>
>> res at cnLevels = (/0.1,0.25,0.5,1.,2.,3.,4.,5.,7.5,10.,12.,14.,16.,18./);
>> the original
>>
>> ;res at cnLevels = (/0.25, 9.3, 11.0, 13.2/)
>>
>>
>> res at gsnMaximize          = True
>>
>> res at gsnPaperOrientation  = "Landscape"
>>
>>
>> res at mpLimitMode = "Corners"
>>
>> res at mpLeftCornerLatF = minlat
>>
>> res at mpLeftCornerLonF = minlon
>>
>> res at mpRightCornerLatF = maxlat
>>
>> res at mpRightCornerLonF = maxlon
>>
>>
>> res at mpFillOn = False ; this will give you a white background
>>
>> res at mpOutlineOn = True                 ; Turn on map outlines
>>
>> res at mpOutlineBoundarySets = "GeophysicalAndUSStates"  ; Turn on US states
>>
>>
>> res at lbBoxLinesOn = False             ; Turn off labelbar box lines
>>
>> res at lbLabelAutoStride = True ; so there aren't overlapping numbers
>>
>> res at lbTitleOn                = True     ; turn on label bar title
>>
>> res at lbTitleString = (PM25data at units)    ; label bar title
>>
>> res at pmLabelBarOrthogonalPosF = .20      ; move label bar down
>>
>>
>> plot = gsn_csm_contour_map(wks,PM25data,res)
>>
>>
>> end   ; end of script
>>
>>
>>
>> Sincerely,
>>
>> Grace
>>
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