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<p class="MsoNormal">Hi folks,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Here is a sequence of events that we are using to download some NARR data from NOMADS at NCDC:<o:p></o:p></p>
<p class="MsoNormal">We use the get-httpsubset.pl script from<o:p></o:p></p>
<p class="MsoNormal"><a href="https://nomads.ncdc.noaa.gov/guide/index.php?name=advanced#adv-httpsubset">https://nomads.ncdc.noaa.gov/guide/index.php?name=advanced#adv-httpsubset</a> and the Perl scripts from<o:p></o:p></p>
<p class="MsoNormal"><a href="http://www.cpc.ncep.noaa.gov/products/wesley/fast_downloading_grib.html">http://www.cpc.ncep.noaa.gov/products/wesley/fast_downloading_grib.html</a> to grab a handful of parameters from the NARR dataset.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This gives us GRIB files like: <o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-a_221_20101201_1200_000.sub.grb">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-a_221_20101201_1200_000.sub.grb</a>
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I then used: ncl_convert2nc narr-a_221_20101201_1200_000.sub.grb -nc4c -l<o:p></o:p></p>
<p class="MsoNormal">To make <o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-a_221_20101201_1200_000.sub.nc4">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-a_221_20101201_1200_000.sub.nc4</a>
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I did this for 30 years of data ending 12-31-2010.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">We then used an NCL script to do some calculations on a month of data, and write the results into a new file.<o:p></o:p></p>
<p class="MsoNormal">Here is the script:<o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/read_narr_ncar-help.ncl">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/read_narr_ncar-help.ncl</a>
<o:p></o:p></p>
<p class="MsoNormal">My apologies to those of you who actually know how to code in NCL. I am strictly an amateur at this.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Here is the file we created: <o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/D-Value_Monthly_Stats.2010.12.averages.1200.nc">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/D-Value_Monthly_Stats.2010.12.averages.1200.nc</a>
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Our problem seems to be aligning the data to the map background, as I can show with the following images:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The grey area in this image is supposed to be where the terrain is higher than the calculated value:<o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-paper.000001.png">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/narr-paper.000001.png</a>
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The data mask area is too far to the west, even extending out over the ocean.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">When we plot it in the Unidata IDV we get what we expect:<o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/IDV_4K_Mask_D-Val.png">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/IDV_4K_Mask_D-Val.png</a>
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Then we decided to try plotting it in Matlab as another test. We got:
<o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/Matlab_Plot_NARR_Mask.jpg">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/Matlab_Plot_NARR_Mask.jpg</a>
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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.)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This can be seen in the following images:<o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/load-both-idv.png">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/load-both-idv.png</a> 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).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">When I open the NetCDF file and plotted MSLP in a window by itself, I got this:<o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/load-netcdf-idv.png">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/load-netcdf-idv.png</a>
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">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.)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The questions I have are:<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="mso-list:Ignore">1)<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>Why does this happen?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="mso-list:Ignore">2)<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>Is this related to my data masking and mapping problem, or are they separate issues?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks in advance for any help on any of these problems/questions.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Cheers,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Chris <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">PS If you want to test our script, there is a month of data in this tar file:<o:p></o:p></p>
<p class="MsoNormal"><a href="http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/sample-narr.tgz">http://wx.erau.edu/faculty/herbster/demo/.hidden/NCL/sample-narr.tgz</a>
<o:p></o:p></p>
<p class="MsoNormal">-- <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Dr. Christopher G. Herbster<o:p></o:p></p>
<p class="MsoNormal">Associate Professor<o:p></o:p></p>
<p class="MsoNormal">Director of Science and Technology<o:p></o:p></p>
<p class="MsoNormal">for the ERAU Weather Center<o:p></o:p></p>
<p class="MsoNormal">Applied Aviation Sciences<o:p></o:p></p>
<p class="MsoNormal">Embry-Riddle Aeronautical Univ.<o:p></o:p></p>
<p class="MsoNormal">600 S. Clyde Morris Blvd.<o:p></o:p></p>
<p class="MsoNormal">Daytona Beach, FL 32114-3900<o:p></o:p></p>
<p class="MsoNormal"><o:p></o:p></p>
<p class="MsoNormal"> 386.226.6444 Office<o:p></o:p></p>
<p class="MsoNormal">386.226.6446 Weather Center<o:p></o:p></p>
<p class="MsoNormal">http://wx.erau.edu/<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Schedule at: http://wx.erau.edu/faculty/herbster/Schedules/<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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