<p>The BRN Shear, which is the denominator of the bulk Richardson number, a parameter used in severe weather forecasting (<a href="https://www.spc.noaa.gov/exper/soundings/help/shear.html" rel="nofollow noreferrer">described here</a>), is (from <a href="https://geo.libretexts.org/Bookshelves/Meteorology_and_Climate_Science/Book%3A_Practical_Meteorology_(Stull)/14%3A_Thunderstorm_Fundamentals/14.04%3A_Section_5-" rel="nofollow noreferrer">Stull's Practical Meteorology</a>):</p>
<p><span class="math-container">$$\mathrm{BRN\;Shear} = 0.5 \cdot (\Delta M)^2$$</span></p>
<p>With <span class="math-container">$\Delta M$</span> defined as:</p>
<p><span class="math-container">$$\Delta M = [(\Delta U)^2 + (\Delta V)^2]^\frac{1}{2}$$</span></p>
<p>where</p>
<p><span class="math-container">$$\Delta U = \overline{U} - U_{SL}\\
   \Delta V = \overline{V} - V_{SL}$$</span></p>
<p>(<span class="math-container">$U$</span>,<span class="math-container">$V$</span>) are wind components from 0 to 6 km 'weighted' average/mean winds.</p>
<p>I would like to ask for some clarification on the <span class="math-container">$U_{SL}$</span> and <span class="math-container">$V_{SL}$</span> terms.  Are these &quot;surface-level&quot; wind components, listed as being from 0 to 0.5 km,  also required to be a weighted average from 0 to 500 m AGL? Or do I only need a 'single' 0.5 km wind acting as the proxy for surface-level winds?</p>

CC BY-SA 4.0
2022-11-07T16:45:12.370Z
Where does your idea for using 0 - 0.5 km come from?  (Not saying it's not true, I don't know BRN particularly, but for the question it kind of poofs out of nowhere!)
JeopardyTempest
CC BY-SA 4.0
2022-11-08T01:18:30.480Z
@JeopardyTempest. Thanks for the comment. It came from this reference https://www.spc.noaa.gov/exper/soundings/help/shear.html. Meanwhile, the whole equation is seen from here 
https://geo.libretexts.org/Bookshelves/Meteorology_and_Climate_Science/Book%3A_Practical_Meteorology_(Stull)/14%3A_Thunderstorm_Fundamentals/14.04%3A_Section_5-
CGHA
CC BY-SA 4.0
2022-11-08T01:54:43.053Z
ok, good deal, I'll edit your question a bit.  But I'm confused what you're asking exactly, as your question "are these surface-level wind components are from 0 to 0.5 km and also being average out" has got some brokenness in the wording.  Can you reread that and see if you can write that better (or if not sure how to, perhaps you can try asking that sentence here in your native language if English isn't your native language)?
JeopardyTempest
CC BY-SA 4.0
2022-11-08T02:28:02.807Z
@JeopardyTempest Thanks. I already edited the question.
CGHA
CC BY-SA 4.0
2022-11-08T03:23:45.753Z
Ok, please make sure that my edit still captures your intent with the question?
JeopardyTempest
CC BY-SA 4.0
2022-11-08T15:39:13.020Z
I am not sure if there is a clear definition on which height you are supposed to use tbh. I find many different ways how people calculate the surface layer windshear. Probably people just use which values they have available. As a rule of thumb I would generally say dont use anything below 100 m because of the influence of the ground. Above 100 m things dont change that much anymore.
smichel
<meteorology><mesoscale-meteorology>
Question on BRN Shear
CGHA
# Question on BRN Shear

(Asked by: username_0 on 2022-11-07)

The BRN Shear, which is the denominator of the bulk Richardson number, a parameter used in severe weather forecasting ([described here](https://www.spc.noaa.gov/exper/soundings/help/shear.html)), is (from [Stull's Practical Meteorology](https://geo.libretexts.org/Bookshelves/Meteorology_and_Climate_Science/Book%3A_Practical_Meteorology_(Stull)/14%3A_Thunderstorm_Fundamentals/14.04%3A_Section_5-)):

$$\mathrm{BRN\;Shear} = 0.5 \cdot (\Delta M)^2$$

With $\Delta M$ defined as:

$$\Delta M = [(\Delta U)^2 + (\Delta V)^2]^\frac{1}{2}$$

where

$$\Delta U = \overline{U} - U\_{SL}\\
\Delta V = \overline{V} - V\_{SL}$$

($U$,$V$) are wind components from 0 to 6 km 'weighted' average/mean winds.

I would like to ask for some clarification on the $U\_{SL}$ and $V\_{SL}$ terms. Are these "surface-level" wind components, listed as being from 0 to 0.5 km, also required to be a weighted average from 0 to 500 m AGL? Or do I only need a 'single' 0.5 km wind acting as the proxy for surface-level winds?

**Tags:** meteorology, mesoscale-meteorology

> **Comments:**
> **username_1**: Where does your idea for using 0 - 0.5 km come from?  (Not saying it's not true, I don't know BRN particularly, but for the question it kind of poofs out of nowhere!)  
> **username_0**: @username_1. Thanks for the comment. It came from this reference https://www.spc.noaa.gov/exper/soundings/help/shear.html. Meanwhile, the whole equation is seen from here  https://geo.libretexts.org/Bookshelves/Meteorology_and_Climate_Science/Book%3A_Practical_Meteorology_(Stull)/14%3A_Thunderstorm_Fundamentals/14.04%3A_Section_5-  
> **username_1**: ok, good deal, I'll edit your question a bit.  But I'm confused what you're asking exactly, as your question "are these surface-level wind components are from 0 to 0.5 km and also being average out" has got some brokenness in the wording.  Can you reread that and see if you can write that better (or if not sure how to, perhaps you can try asking that sentence here in your native language if English isn't your native language)?  
> **username_0**: @username_1 Thanks. I already edited the question.  
> **username_1**: Ok, please make sure that my edit still captures your intent with the question?  
> **username_2**: I am not sure if there is a clear definition on which height you are supposed to use tbh. I find many different ways how people calculate the surface layer windshear. Probably people just use which values they have available. As a rule of thumb I would generally say dont use anything below 100 m because of the influence of the ground. Above 100 m things dont change that much anymore.  

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## 0 answers

