# [ncl-talk] Brown's indicator

Lyndz olagueralyndonmark429 at gmail.com
Thu May 30 05:58:12 MDT 2019

```Hi,

I suggest looking at the following resources to compute this. Take note of
the version of NCL used in these resources.

[1] For computing shear and stretching deformation:
https://www.ncl.ucar.edu/Document/Functions/Contributed/shear_stretch_deform.shtml

[2] For computing absolute vorticity:
First compute the relative vorticity using spherical harmonics:
https://www.ncl.ucar.edu/Applications/vort.shtml

Then, you can add the coriolis parameter this way:

vr = vr + *conform*
<http://www.ncl.ucar.edu/Document/Functions/Built-in/conform.shtml>(vr,
flat, 2) )    ; flat matched the '2-th' dimension of 'vr'
vr at long_name = "absolute vorticity"
vr at units     = "per second
*copy_VarCoords*
<http://www.ncl.ucar.edu/Document/Functions/Contributed/copy_VarCoords.shtml>(u,
vr)

[3] NCL also provides a way to compute the coriolis parameter:
https://www.ncl.ucar.edu/Document/Functions/Contributed/coriolis_param.shtml

or you can also do it this way:

W   = 7.292e-5                   ; (1/s)     ; earth ang rotation
f   = 2.*W*sin(lat*rad)          ; (1/s)     ; coriolis parameter

Then, applying Brown's indicator equation is pretty straighforward.

Sincerely,

*Lyndz*

On Thu, May 30, 2019 at 7:32 PM Ehsan Taghizadeh <ehsantaghizadeh at yahoo.com>
wrote:

> Dears,
> I hope this email finds you well.
> As you know, there is various indicators for CAT (Clear Air Turbulence),
> like *Richardson number (Ri)* or *Brown's indicator*, etc. I've found
> attached script for *Ri*. May I ask if anyone has any script to compute *Brown's
> indicator*, or other CAT indicators in NCL?
> I'll be thankful if I hear from you.
> Sincerely
> Ehsan
>
> [image: Inline image]
>
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