# [ncl-talk] About wrf_user_intrp3d to get cross section of wind vector.

Tue Feb 14 10:13:52 MST 2017

```Hi Tao,

When you do a vertical cross section, you are defining a line along the
surface and the algorithm interpolates to a vertical plane along that
line.  The line on the surface can be defined by using a start point and an
end point, or a pivot point and an angle.  So, if you are using the pivot
point and angle, to define a S-N cross section through the entire domain,
you want to set the pivot point to the center of the domain and the angle
to be 0.0.  To define a W-E cross section through the entire domain, you
would set the pivot point to the center of the domain and the angle to be
90.0.

1) If you don't provide the same cross-section line to all three wind
components, you won't be using the same cross-section, which is going to be
nonsensical.

2) I think you may be misunderstanding what this function is doing.  This
algorithm doesn't find the wind components aligned with the orientation of
the cross section, it simply goes point by point along the line at the
surface, and for a fixed number of vertical points determines the value at
these points by doing a linear interpolation in the vertical.  The u_plane
component is still the west_east component, the v_plane component is still
the south_north component, and the w_plane component is still the
bottom_top component.

Hope this helps,

Bill

On Mon, Feb 13, 2017 at 1:44 AM, Tao Lu <hakufu.asano at gmail.com> wrote:

> Hello,
>
> I want to get cross section of vertical wind vector.
> We need this function to interpolate
>
> 	function wrf_user_intrp3d (
> 		var3d      : numeric,
> 		vert       : numeric,
> 		plot_type  : string,
> 		loc    [*] : numeric,  ; up to four values
> 		angle      : numeric,
> 		res    [1] : logical
> 	)
>
> u_plane := wrf_user_intrp3d(u,z,"v",plane,angle,opts)
> v_plane := wrf_user_intrp3d(v,z,"v",plane,angle,opts)
> w_plane := wrf_user_intrp3d(w,z,"v",plane,angle,opts)
>
> If I want to S-N section, i should set angle=0?
> And make vector like this
> vector = wrf_vector(a,wks,v_plane,w_plane,opts)?
> [image: Inline image 1]
> So here I have two questions:
> 1. Why should all of u_plane, v_plane, w_plane set the same angle?
> 2. When we make vector plot vector = wrf_vector(a,wks,v_plane,w_
> plane,opts):
>    In my opinion, if you want S-N plane vector you should use v_plane and
> w_plane. If you want W-E, you should use u_plane and w_plane.
>    But I see some codes, they always use u_plane and w_plane whether they
> do S-N or W-E plot. Why?
>
> Tao
>
> --
> ******************************************************
> 盧 涛 (ル タオ) 修士課程2年
>
> 〒112-8551 東京都文京区春日1-13-27
>
> 中央大学理工学研究科都市環境学専攻
>
> 河川・水文研究室（山田正教授）
>
>
> TEL: 03-3817-3406;   Phone: 070-2188-7509
> Email1: hakufu.asano at gmail.com <mail%3Amet.yamos at gmail.com>
> Email2: lutao at civil.chuo-u.ac.jp <mail%3Ayamoto at civil.chuo-u.ac.jp>
> *******************************************************
> ******************************************************
> Tao Lu    (M. Eng)
> Laboratory of River Engineering and Hydrology,
> Dept. of Civil and Environmental Engineering,
> Graduate School of Science and Engineering,
> Chuo University
>
> 1-13-27,Kasuga,Bunkyo-ku,Tokyo
> 112-8551, Japan
> TEL: 03-3817-1805;   Phone: 070-2188-7509
> Email1: hakufu.asano at gmail.com <mail%3Amet.yamos at gmail.com>
> Email2: lutao at civil.chuo-u.ac.jp <mail%3Ayamoto at civil.chuo-u.ac.jp>
> *****************************************************
>
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