[ncl-talk] Problem aligning data with map

[Rick Brownrigg]

Hi,

Is it possible to make this file available too, in order to run the script:

AWIP32-fixed.grb

Rick

On Tue, Mar 27, 2018 at 3:02 PM, Herbster, Christopher G. <herbstec at erau.edu
> wrote:

> Hi folks,
>
>
>
> Here is a sequence of events that we are using to download some NARR data
> from NOMADS at NCDC:
>
> We use the get-httpsubset.pl script from
>
> https://nomads.ncdc.noaa.gov/guide/index.php?name=advanced#adv-httpsubset
> and the Perl scripts from
>
> http://www.cpc.ncep.noaa.gov/products/wesley/fast_downloading_grib.html
> to grab a handful of parameters from the NARR dataset.
>
>
>
> This gives us GRIB files like:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/
> narr-a_221_20101201_1200_000.sub.grb
>
>
>
> I then used: ncl_convert2nc narr-a_221_20101201_1200_000.sub.grb -nc4c -l
>
> To make
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/
> narr-a_221_20101201_1200_000.sub.nc4
>
>
>
> I did this for 30 years of data ending 12-31-2010.
>
>
>
> We then used an NCL script to do some calculations on a month of data, and
> write the results into a new file.
>
> Here is the script:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/
> read_narr_ncar-help.ncl
>
> My apologies to those of you who actually know how to code in NCL.  I am
> strictly an amateur at this.
>
>
>
> Here is the file we created:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/D-
> Value_Monthly_Stats.2010.12.averages.1200.nc
>
>
>
> Our problem seems to be aligning the data to the map background, as I can
> show with the following images:
>
>
>
> The grey area in this image is supposed to be where the terrain is higher
> than the calculated value:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-paper.000001.png
>
>
>
> The data mask area is too far to the west, even extending out over the
> ocean.
>
>
>
> When we plot it in the Unidata IDV we get what we expect:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/IDV_4K_Mask_D-Val.png
>
>
>
> Then we decided to try plotting it in Matlab as another test.  We got:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/
> Matlab_Plot_NARR_Mask.jpg
>
>
>
>
>
> While I suspect that I am not doing something properly with the mapping of
> the data, I am also wondering about the results of making the NetCDF file
> from the ncl_convert command.
>
>
>
> First, is the compression lossy?  I realized that the default compression
> is zero, so this step did not do much for disk space!  (Actually made
> bigger files, but never mind.)
>
>
>
> When I load the original GRIB file into the IDV it displays the region
> properly without any problem.  When I try to load the original NetCDF file,
> the IDV does not seem to know the geographic region of the data.
>
>
>
> This can be seen in the following images:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/load-both-idv.png
> shows the Mean Sea Level Pressure data from both files.  They appear to
> match.  However, when I added the second panel (NetCDF file), the IDV did
> not display the data properly, and did so only after I selected a
> predefined CONUS projection (as shown).
>
>
>
> When I open the NetCDF file and plotted MSLP in a window by itself, I got
> this:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/load-netcdf-idv.png
>
>
>
> I had to zoom way out to display this data.  It knows where to put the
> data, but the IDV thinks the data should be in the white box area, I
> think.  (I’m not really sure about this interpretation.)
>
>
>
> The questions I have are:
>
> 1)      Why does this happen?
>
> 2)      Is this related to my data masking and mapping problem, or are
> they separate issues?
>
>
>
> Thanks in advance for any help on any of these problems/questions.
>
>
>
> Cheers,
>
>
>
> Chris
>
>
>
> PS  If you want to test our script, there is a month of data in this tar
> file:
>
> http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/sample-narr.tgz
>
> --
>
>
>
> Dr. Christopher G. Herbster
>
> Associate Professor
>
> Director of Science and Technology
>
> for the ERAU Weather Center
>
> Applied Aviation Sciences
>
> Embry-Riddle Aeronautical Univ.
>
> 600 S. Clyde Morris Blvd.
>
> Daytona Beach, FL 32114-3900
>
>  386.226.6444 <(386)%20226-6444> Office
>
> 386.226.6446 <(386)%20226-6446> Weather Center
>
> http://wx.erau.edu/
>
>
>
> Schedule at:  http://wx.erau.edu/faculty/herbster/Schedules/
>
>
>
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