[ncl-talk] diagonal cross section with wrf_user_intrp3d

[Evelyn Grell - NOAA Affiliate]

Matthew,

Regarding your second question (the easier one), I got confused by this
too.  I believe the order of the variables got changed between versions:
In v6.1.2, the order to specify 2 points for a cross section has to be
x1,x2,y1,y2.
In v6.2.1, the order to specify 2 points has to be x1,y1,x2,y2.
(maybe wrfhelp could add a note in the example.)

You can check by looking at the code in your
$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl

Another thing that I ran into is that it assumes you are defining your
points in "WRF" space (ie arrays start with 1) rather than in "NCL" space
(ie arrays start with 0) so it subtracts 1 for you...

In wrf_user_interp3d:

; set vertical cross section
     if (opts) then
       xy = wrf_user_set_xy( z, loc_param(0)-1, loc_param(2)-1, \    ;
the -1 is for NCL dimensions
                                loc_param(1)-1, loc_param(3)-1, \
                                angle, opts )

(loc_param is the variable containing your XS endpoints).

About your first question, maybe you are missing the 2d interpolation that
defines the x-axis?

something like:
    if (xang.gt.20. .and. xang.lt.340) then
      X_plane = wrf_user_intrp2d(lon,xspts,0.,True)
    else
      X_plane = wrf_user_intrp2d(lat,xspts,0.,True)
    end if
    dimsX = dimsizes(X_plane)
    xspan = dimsX(0)-1

     res at tmXBValues              = fspan(0,xspan,2)

Hope that helps,
Evelyn Grell


On Mon, Mar 23, 2015 at 12:21 AM, Matthew Fearon <Matthew.Fearon at dri.edu>
wrote:

>  Dear WRF-help and NCL users,
>
> Has anyone successfully plotted a cross section with wrf data
> along a diagonal, say southeast to northwest or vice versa, using
> wrf_user_intrp3d? North/south or east/west works fine, but from the
> documentation, a diagonal seemed possible using the example below
> *, *although I can't get it working
>
> *? *Also, the plane is defined (/xstart,xend , ystart,yend/) for sure
> rather than (/xstart,ystart , xend,yend/) instead?
>
> thanks,
> Matt
>
>
>
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>   load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"*
>
>   a = addfile <https://www.ncl.ucar.edu/Document/Functions/Built-in/addfile.shtml>*("wrfout_d01_2000-01-24_12:00:00.nc","r")
>
>   time = 1
>   tc = *wrf_user_getvar* <https://www.ncl.ucar.edu/Document/Functions/WRF_arw/wrf_user_getvar.shtml>(a,"tc",time)   ; T [C]
>   z  = *wrf_user_getvar* <https://www.ncl.ucar.edu/Document/Functions/WRF_arw/wrf_user_getvar.shtml>(a,"z",time)    ; z on mass points
>
>   plane = (/  40,81 , 259,81  /) ; approx. START x;y and END x;y point
>
>   ; Extract cross section from point A to point B, as defined in "plane"
>   ; And vertically interpolate to height coordinates ("z")
>   tc_plane = *wrf_user_intrp3d*(tc,z,"v",plane,0.,True)
>
>
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