[ncl-talk] how to change tickmark to standard pressure levels in WRF cross-section plot

[Bill Ladwig]

Hi Richard,

An easy way to modify the routine without breaking your installation is to
create a new file (e.g. myfile.ncl), then copy the wrf_user_intrp3d routine
from WRFUserARW.ncl in to this file.  Modify your copy of wrf_user_intrp3d
to set the levels that you want.  This will be around line 370, and the
current code looks like:

;  interp to constant z grid
>      if(var2dz(0,0) .gt. var2dz(1,0) ) then  ; monotonically decreasing
> coordinate
>         z_max = floor(max(z)/10)*10     ; bottom value
>         z_min = ceil(min(z)/10)*10      ; top value
>         dz = 10
>         nlevels = tointeger( (z_max-z_min)/dz)
>         z_var2d = new( (/nlevels/), typeof(z))
>         z_var2d(0) = z_max
>         dz = -dz
>      else
>         z_max = max(z)
>         z_min = 0.
>         dz = 0.01 * z_max
>         nlevels = tointeger( z_max/dz )
>         z_var2d = new( (/nlevels/), typeof(z))
>         z_var2d(0) = z_min
>      end if
>
>      do i=1, nlevels-1
>         z_var2d(i) = z_var2d(0)+i*dz
>      end do


You'll want to set z_var2d to be the levels that you want, and comment out
the rest.  Hopefully everything else will just work.  Finally, at the top
of your plotting script, do:

load "/path/to/myfile.ncl"


where the "/path/to" is the path to where the myfile.ncl is located on your
system.  As long as you have the "undef("wrf_user_intrp3d")" above your
definition of wrf_user_intrp3d in myfile.ncl, this will clobber the
WRFUserARW.ncl version.  Note that in recent versions of NCL,
WRFUserARW.ncl is loaded by default, so you don't need load statements for
it anymore.  The only load statement you should need is the one shown above.

The ability to set your own cross section levels will be coming in a future
release.  Currently wrf-python supports this, but it needs to get ported
back to NCL.

Hope this helps,

Bill

On Thu, Nov 23, 2017 at 10:07 PM, music piano <musicpianoljy at gmail.com>
wrote:

>
>
> Hi, Everyone
>
> Example is here
> http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/Exa
> mples/CROSS_SECTION/wrf_CrossSection3.htm
>
> The tickmarks here are 1010, 960, 910...... But I want standard levels
> such as 1000, 950, 900.....
>
> My analysis of the code is as follow:
> (1)
> rh_plane = wrf_user_intrp3d(rh,p,"v",plane,0.,opts)
>
> It interpolates the data into pressure coordinate. However, the pressure
> levels are not standard levels as I check the subroutine "WRFUserARW.ncl"
> . It begins with the highest pressure from the bottom, not from 1000. Thus,
> the tickmark position represents nonstandard pressure
>
> (2) opts_xy at tmYLMode = "Explicit"
> opts_xy at tmYLValues = fspan(0,zspan,nz) opts_xy at tmYLLabels =
> sprintf("%.0f",fspan(zmin,zmax,nz))
>
> give labels to each tickmark position. Since the tickmark position is not
> in standard pressure, it shows 1010, 960.....
> I have tried to use @ tmYLMode ="Manual"  *tmYLTickStartF
> <https://www.ncl.ucar.edu/Document/Graphics/Resources/tm.shtml#tmYLTickStartF> *,
> or set trXMaxF , none of them works. They still plot tickmark position.
>
> I can possibly modify "WRFUserARW.ncl to let it interpolation to standard
> levels, but that may require reinstalling NCL in the machine, which is hard.
>
> Does anyone know how to produce tickmarks which specify the standard
> pressure value?
>
> Thank you very much
> Richard
>
>
>
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