[ncl-talk] Cross sections w/ smoothed terrain.... New issue???

Bill Ladwig ladwig at ucar.edu
Thu Apr 12 11:05:25 MDT 2018 

Hi Kacie,

Rick and I both looked over this problem and came up with a solution, but
you won't be able to use the wrf_contour routines with it. You have to use
the gsn_csm_contour routines instead. The root cause of the problem is that
the example you are using does a bit of a hack to get the RH contours on to
a scatter plot for terrain. It tries to cap the height of the terrain plot
to a value that you specify (i.e. zmax), then tries to crop the data for RH
to fit in that terrain scatter plot area. To make a long story short, as
you go higher up in WRF, the grid boxes get taller. When cropped, there's a
bunch of extra slop depending on how the WRF grid aligns with the zmax you
chose, since the chosen value for zmax might be in the middle of a grid
box. At the end of the day, there's going to be misalignment between the
contour plot for terrain and the contour plot of RH, since those contours
aren't being drawn with an identical y-axis. The example page warns of this
with "Users are *STRONGLY CAUTIONED* that these scripts are EXPERIMENTAIL
and the terrain may not plot in exactly the right location.".

To fix the problem, we're going to supply the RH cross section with
coordinate data for the "Vertical" dimension. Once the RH cross section has
the height information, it's easy for NCL to plot the terrain and RH on the
same y-axis. (Not having the cross section height coordinate information is
the real cause of this problem and why the hack was required for the
example you used. In the future, I will be adding a new cross section
routine to NCL that mirrors what wrf-python is doing, so these kind of
plots will be easier in the future.)

Attached is a script (new_cross_section.ncl) that shows how we did it. Note
that if you decide you still want to modify WRFUserARW.ncl to improve the
vertical resolution of the cross section (as we did), you'll also need to
modify new_cross_section.ncl to match. I've attached the modified
WRFUserARW.ncl that we used for version 6.4.0 (make sure you copy the
WRFUserARW.ncl that came with your NCL distribution if you aren't using
6.4.0). You can just keep the modified version of WRFUserARW.ncl in the
same directory as new_cross_section.ncl and the script will load it at the
top.

The plots I attached below show the cross sections for the original data
(contour_rh) and the data with the missing values filled (contour_rh2) so
you can see the differences. The script itself is still a bit messy, but I
removed most of the stuff that wasn't needed to make these plots. Let me
know if you have any questions.

Hope this helps,

Bill


On Mon, Apr 9, 2018 at 12:05 PM, Kacie Shourd <Kacie.Shourd at dri.edu> wrote:

> Hi everyone,
>
> It's been a while since anyone posted to this thread, but I tried the
> suggested fix (modifying my WRFUserARW.ncl line 382) to no avail! There is
> still a good chunk of data missing above the terrain. See the attached
> output images. The wider image is the default with "dz=0.01*z_max" and the
> skinnier image is with "dz=0.00001*z_max".
>
> Attempted fix:
>
> "Have you modified line ~382 in WRFUserARW.ncl yet?  dz can be decreased
> from the default value of 0.01:
>
> ...else
>         z_max = max(z)
>         z_min = 0.
> *; Changed to:*
> *dz = 0.00001 * z_max*
>         ; From:
> *        ;dz = 0.01 * z_max*
>         nlevels = tointeger( z_max/dz )
>         z_var2d = new( (/nlevels/), typeof(z))
>         z_var2d(0) = z_min
>      end if"
>
> There are quite noticeable differences between the two plots, but no
> improvement to the terrain. I am close to giving up on this, but thought I
> would reach out one more time. I have changed other things in the
> "wrf_intrpd_3d" function also without luck. As mentioned before, the
> missing data near the terrain was not an issue in a colleague's RIP plot,
> so I know it is not the data.
>
> Best,
> Kacie
>
> ---
>
> Kacie N. Shourd, M.S.
> 드림
>
> Staff Research Scientist
> Division of Atmospheric Science
> Desert Research Institute, Reno, NV
> Kacie.Shourd at dri.edu
> Work: (775) 674-7049
> ------------------------------
> *From:* Scott Capps [scapps at atmosdatasolutions.com]
> *Sent:* Tuesday, March 27, 2018 4:47 PM
> *To:* Kacie Shourd
> *Cc:* ncl-talk (ncl-talk at ucar.edu)
> *Subject:* Re: [ncl-talk] Cross sections w/ smoothed terrain.... New
> issue???
>
> Have you modified line ~382 in WRFUserARW.ncl yet?  dz can be decreased
> from the default value of 0.01:
>
> ...else
>         z_max = max(z)
>         z_min = 0.
> ; Changed to:
> dz = 0.002 * z_max
>         ; From:
>         ;dz = 0.01 * z_max
>         nlevels = tointeger( z_max/dz )
>         z_var2d = new( (/nlevels/), typeof(z))
>         z_var2d(0) = z_min
>      end if
>
> On Tue, Mar 27, 2018 at 4:36 PM, Kacie Shourd <Kacie.Shourd at dri.edu>
> wrote:
>
>> Hi NCL friends,
>>
>> Attached is an image of the current output I am getting trying to plot a
>> vertical cross section with WRF data in NCL. Also attached is my code, and
>> I can upload the WRF data file for anyone who needs it.
>>
>> I have used this script tons of times in the past with no issue (i.e. no
>> "missing" data near the ground, or at least the terrain was smoothed to
>> cover that up) and am hoping to figure out what's wrong.
>>
>> Could it be the data file I have? If yes, is there a simple way I can
>> extrapolate the RH values to below the ground?
>>
>> Is it the version of NCL I am running?? I used to run this script in v6.4
>> but am using v6.3 at the moment.
>>
>> A colleague of mine made a plot with the same WRF file in RIP and did not
>> have this issue. I would prefer to plot this up in NCL if possible as I
>> think the plots come out nicer and this is going into a document for some
>> pretty important folks...
>>
>> Thanks,
>> Kacie
>>
>> ---
>>
>> Kacie N. Shourd, M.S.
>> 드림
>>
>> Staff Research Scientist
>> Division of Atmospheric Science
>> Desert Research Institute, Reno, NV
>> Kacie.Shourd at dri.edu
>> Work: (775) 674-7049
>>
>> PUBLIC RECORDS NOTICE: In accordance with NRS Chapter 239, this email and
>> responses, unless otherwise made confidential by law, may be subject to the
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>>
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>>
>
>
> --
> *Scott Capps*
> Principal
> Atmospheric Data Solutions
> <https://linkprotect.cudasvc.com/url?a=http://www.atmosphericdatasolutions.com&c=E,1,ii7FITA5DOfDJKepvgGfOku-AGID3DnAJtS5iWd_oBwb_PIKnfs-1V1XTcN2ZiESPh4EGugxUHZb3Vv0bmuUu2W6sV9LogTv0Nw4PDekVE-r4rFAJI2KDnz5K5wQ&typo=1>
> scapps at atmosdatasolutions.com
> cell: (949) 910-4385
>
>
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