# [ncl-talk] wrf_user_interp_level

Fri Sep 17 04:04:03 MDT 2021

```Dear NCL Community,
I want to interpolate the zonal wind in the wrfout-data to a height of 100m from the ground.
I use the function 'wrf_user_interp_level'.
Before interpolation, the data of all grid points have a value. After the interpolation, the data of one grid point is the default value. After checking, I found that the data at the height of 100m from the grid point to the ground can be obtained without interpolation, so I would like to ask you if there is a problem with this function.
My NCL version is 6.6.2. The script runs without errors.

My script is:
begin
a=addfile("wrfout_d01_2005-12-20_00:00:00.nc","r")
u = wrf_user_getvar(a,"ua",-1)
z = wrf_user_getvar(a,"z",-1)
hgt = a->HGT
dimll=dimsizes(z)
hfg=new((/dimll(0),dimll(1),dimll(2),dimll(3)/),float)
copy_VarMeta(z, hfg)

do time=0,dimll(0)-1
do lev=0,dimll(1)-1
do jj=0,dimll(3)-1
do ii=0,dimll(2)-1
hfg(time,lev,ii,jj)=z(time,lev,ii,jj)-hgt(time,ii,jj)
end do
end do
end do
end do

u_plane = wrf_user_interp_level(u,hfg,100.,False)
loc = wrf_user_ll_to_ij(a,95.5,33,True)
locX = loc(0) - 1
locY = loc(1) - 1
print(u(3,:,locY,locX-1))
print(u_plane(3,locY,locX-1))
print(hfg(3,:,locY,locX-1))
end

And the result is:

You see, hfg(3)=100, and it is the _FillValue when the zonal wind is interpolated to 100m，but u(3)=9.758717. And u(3) is the value obtained by interpolating the zonal wind to a height of 100m above the ground. So I would like to ask if this is the problem with the interpolation function?

Any hint is much appreciated!
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```

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