# [ncl-talk] Azimuthal average of vertical velocity

Dennis Shea shea at ucar.edu
Fri May 10 16:41:10 MDT 2019

```For sure, the [nice] plot was generated by NCL [panel plot with common
labelbar].
---
There was a 2017 thread on this topic. A rough approach [tst_polar.ncl] was
I cleaned it up and made it a function. A pic of the methodology used by
the function (or tries to do) is here:

; A conceptual sketch: A pic:
;
*https://cs.stackexchange.com/questions/43744/fast-algorithm-for-interpolating-data-from-polar-coordinates-to-cartesian-coordi*
<https://cs.stackexchange.com/questions/43744/fast-algorithm-for-interpolating-data-from-polar-coordinates-to-cartesian-coordi>

This works in degrees not km.

However, if your convert the 'radius' [degrees] to those that coincide with
km distance, this should work!  I hope!!!

The attached uses *random data *so the plot [azimuthal_avg.png] does not
look too good.
=====

A better function would use "*geolocation_circle*
<https://www.ncl.ucar.edu/Document/Functions/Contributed/geolocation_circle.shtml>
"
This optionally allows 'degrees' or 'km' as input and would allow for *much*
higher spatial sample at each radii.
Some example of its use are at:

*https://www.ncl.ucar.edu/Applications/polyg.shtml*
<https://www.ncl.ucar.edu/Applications/polyg.shtml>
Examples*:*

*polyg_24, polyg_25*
*polyg_29, polyg_30 and polyg_31*

Good luck

On Fri, May 10, 2019 at 7:19 AM David Warner <davidwarnerdavid1992 at gmail.com>
wrote:

> [image: image.png]
>
> On Fri, May 10, 2019 at 6:46 PM David Warner <
> davidwarnerdavid1992 at gmail.com> wrote:
>
>> Dear NCL community,
>>
>> Is there any function available in NCL to compute the azimuthal average of a 3D variable.
>>
>> For example, I need to plot something similar to the image displayed which is the height-radius crosssection of azimuthal average of vertical velocity.
>>
>> Given the lat and lon locations by the user, the function must compute the azimuthal mean of the variable.
>>
>> Any suggestions would be highly appreciated. Kindly reply at your earliest convenience.
>>
>>
>> [image: image.png]
>> (Image courtesy: Hui Wang et al., 2014)
>>
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