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

Tao Lu hakufu.asano at gmail.com
Tue Feb 14 16:10:29 MST 2017

```Hi Bill,

Thank you for your great explanation.

Especially the second one 2), it really helps me a lot.
Now, I am released.

Thank you again.

Tao

On Wed, Feb 15, 2017 at 2:13 AM, Bill Ladwig <ladwig at ucar.edu> wrote:

> 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_pla
>> ne,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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>

--
******************************************************

〒112-8551 東京都文京区春日1-13-27

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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