[ncl-talk] wrf_user_intrp3d always interpolates to 100 levels

Bill Ladwig ladwig at ucar.edu
Fri Dec 15 10:30:37 MST 2017 

The current cross section implementation in NCL does not allow the user to
select the levels to interpolate to.  The 'z' argument is not the levels
that you want, it's the height coordinate value for each grid point (either
pressure or geopotential height).  In a future release, we will be creating
a new vertical cross section function that has the same capabilities as
wrf-python (which does have the capability you want).  For now, if you want
to modify your WRFUserARW.ncl to specify the levels that you want, you need
to modify this (around line 371):

;  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


Set z_var2d to be the levels that you want and comment out the rest.  If
you don't want to modify the original WRFUserARW.ncl code, then copy
wrf_user_intrp3d to a new file (and either change the function name or
remember to call undef("wrf_user_intrp3d") before the function definition)
and use a load statement at the top of your script.

Hope this helps,

Bill

On Fri, Dec 15, 2017 at 7:31 AM, Trostel, John M. <
john.trostel at gtri.gatech.edu> wrote:

> This should have read:
>
>
> When using the function to produce a cross section ALONG A RADIAL IN THE
> X/Y PLANE...
>
>
> Sorry for any confusion.
>
>
> --
> John Trostel
> Director - Severe Storms Research Center
> Georgia Tech Research Institute
> Atlanta, GA 30332-0857
> ------------------------------
> *From:* ncl-talk <ncl-talk-bounces at ucar.edu> on behalf of Trostel, John
> M. <john.trostel at gtri.gatech.edu>
> *Sent:* Friday, December 15, 2017 9:23:39 AM
> *To:* Barry Lynn
>
> *Cc:* ncl-talk at ucar.edu
> *Subject:* Re: [ncl-talk] wrf_user_intrp3d always interpolates to 100
> levels
>
>
> When using the function to produce a cross section, the plane is oriented
> in the vertical direction.  One of the inputs is a height/z array.  The
> code ignores all but the min/max of this array and just interpolates to 100
> evenly spaced points in this vertical plane.
>
>
> I have a very inelegant hack of the function working in my custom version
> of WRFUserARW.ncl.  In the hacked version, the input z array is used to
> produce the vertical dimension of the output.  The interpolation, is purely
> in the horizontal plane.
>
>
> If the function is used to produce a vertical plane, the interpolation is,
> as you mentioned, to that constant height.
>
>
> --
> John Trostel
> Director - Severe Storms Research Center
> Georgia Tech Research Institute
> Atlanta, GA 30332-0857
> ------------------------------
> *From:* Barry Lynn <barry.h.lynn at gmail.com>
> *Sent:* Friday, December 15, 2017 3:21:29 AM
> *To:* Trostel, John M.
> *Cc:* ncl-talk at ucar.edu
> *Subject:* Re: [ncl-talk] wrf_user_intrp3d always interpolates to 100
> levels
>
> Dear John:
>
> I am not sure I follow what you are trying to do, but plane should be a
> single number, like the height you want to interpolate to (in m, if z is in
> m).
>
> Barry
>
> On Thu, Dec 14, 2017 at 11:24 PM, Trostel, John M. <
> john.trostel at gtri.gatech.edu> wrote:
>
>> I have been trying to use the function “wrf_user_intrp3d”  and assumed it
>> would work like the NCL documentation suggests.
>>
>>
>>
>> Function wrf_user_intrp3d (var3d, vert, plot_type, loc, angle, logical)
>>
>>
>>
>> I am calling it as follows:
>>
>>                 rh_plane = wrf_user_intrp3d(rh,z,"v",plane,0.,opts)
>>
>>
>>
>> where rh is my relative humidity variable from wrfout (at time “it)
>>
>> rh = wrf_user_getvar(a,"rh",it)      ; relative humidity
>>
>> and z is my model heights
>>
>> z   = wrf_user_getvar(a, "z",it)     ; grid point height
>>
>> plane is defined as follows:
>>
>>
>>
>> ; Find the ij location for the Test Site (remains constant)
>>
>> test_lat = 35.0
>>
>> test_lon = -85.7
>>
>> llres = True
>>
>> llres at ReturnInt = True   ; Return integer values
>>
>> locij = wrf_user_ll_to_ij(a, test_lon, test_lat, llres)
>>
>> locij = locij - 1        ; array pointers in NCL space
>>
>> TestX = locij(0)
>>
>> TestY = locij(1)
>>
>> ;               print("TestX (" + test_lat + "): " + TestX)
>>
>> ;               print("TestY (" + test_lon + "): " + TestY)
>>
>>
>>
>> ; Find the ij location for the end point (change for different arcs)
>>
>> end_lat = 34.0
>>
>> end_lon = -85.5
>>
>> llres = True
>>
>> llres at ReturnInt = True   ; Return integer values
>>
>> locij = wrf_user_ll_to_ij(a, end_lon, end_lat, llres)
>>
>> locij = locij - 1        ; array pointers in NCL space
>>
>> EndX = locij(0)
>>
>> EndY = locij(1)
>>
>>
>>
>>                 plane = new(4,float)
>>
>>                 plane = (/ TestX, TestY, EndX, EndY /)    ; start x;y &
>> end x;y point
>>
>>
>>
>> and, finally
>>
>>                 opts=True
>>
>>
>>
>> I would expect to get back rh_plane values along the radial of the
>> defined “plane” at the heights specified in z.  In this case, I defined 50
>> heights for WRF, so I have a nZ of 50 for the z/interpolation variable.   I
>> was baffled when I got back 100 rh_plane values in the vertical.  Looking
>> through the source code for wrf_user_intrp3d (finally), I found that the
>> function is just interpolating to a uniform 100 levels between the min and
>> max Z values.
>>
>>                 z_max = max(z)
>>
>>                 z_min = 0.
>>
>>                 dz = 0.01 * z_max
>>
>>                 nlevels = tointeger( zmax/dz )
>>
>>
>>
>> Why doesn’t the routine use the levels that the user has input into the
>> function?
>>
>> Is there an improved wrf_user_intrp3d function? (Can I fix it and
>> recompile it easily?)
>>
>>
>>
>> --
>>
>> John Trostel
>>
>> Director – Severe Storms Research Center
>>
>> Georgia Tech Research Institute
>>
>> Atlanta, GA 30332-0857
>>
>>
>>
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>>
>>
>
>
> --
> Barry H. Lynn, Ph.D
> Senior Lecturer,
> The Institute of the Earth Science,
> The Hebrew University of Jerusalem,
> Givat Ram, Jerusalem 91904, Israel
> Tel: 972 547 231 170
> Fax: (972)-25662581
>
> C.E.O, Weather It Is, LTD
> Weather and Climate Focus
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>
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