<p>I would like to ask about horizontal wind shear. In most cases, we frequently talk about vertical wind shear (VWS), which is the change in wind speed and direction with height or within a given layer/depth of the atmosphere. I understand that VWS is calculated typically as a vector difference between wind velocities at different levels in the atmosphere, say between the 850 hPa and 200 hPa pressure levels.</p>
<p>What I'm wondering about is: how can I calculate <em>horizontal</em> wind shear (HWS)? I'm interested in calculating and visualizing how wind velocities change along the horizontal or parallel to the Earth's surface, preferably via Python given gridded data (esp. reanalysis), especially in phenomena where there are sharp changes in wind velocity (esp. shear lines, but also in true fronts). Since we calculate VWS along an axis (i.e. along the vertical axis), I assume that HWS should also be calculated along an axis, but which axis exactly? Would it be North-South (meridional) or East-West (zonal), or both (like components being combined into a vector)? And how do I calculate the vector differences? Would it be in between points, or in between lines or latitude/longitude?</p>

CC BY-SA 4.0
2024-11-13T00:54:18.493Z
Are you asking how to visualize a vector field, or solving an equation to obtain a sheared wind vector field, or do you want real data on wind velocities and obtain your shear from this data? Very unclear question at the moment.
AtmosphericPrisonEscape
CC BY-SA 4.0
2024-11-13T07:24:01.260Z
I mean you'd calculate it the same way vertical wind shear is calculated... you'd have a horizontal (or pseudo-horizontal if aloft) grid of winds.  You could calculate the difference in vectors between neighboring "x" gridpoints and neighboring "y" gridpoints (and probably diagonally too, to x+1, y+1, to get the fullest field).  I'm sure there are basic functions/packages available to do vector calculations.
JeopardyTempest
CC BY-SA 4.0
2024-11-13T07:30:05.837Z
But I'd think in typical meteorological data, you'll get a horizontal shear that is poorly representative of the values needed for like aviation.  Because the resolution of global and even mesoscale models are quite a few miles/km.  And the biggest issues are much more localized (convective downbursts and such).  For things like planes, or situations that like do damage or such, you need the change over like 100 meters or less.  Whereas the models will be the difference averaged over 3 km or much more.  Plus the coarser gridscale means the peak values will be blurred out in each grid point too
JeopardyTempest
CC BY-SA 4.0
2024-11-13T07:42:05.937Z
Reanalysis is often even worse (I see NCAR has a 2.5° field!  A degree is 111 km/69 miles.  So where you're typically looking for sharp differences over a tiny distance, you're instead only seeing the gradual synoptic differences between states/countries).  If you want an estimate of true potential horizontal shear from reanalysis/global/mesoscale models, I'd believe the only option would be developing analysis equations upon key widescale factors to estimate the possibility of certain shear levels.  Think that's how turbulence, microburst, etc forecasting is typically done regionally.
JeopardyTempest
CC BY-SA 4.0
2024-11-15T15:14:50.683Z
You can take a look at the equation for the horizontal shear here - https://math.stackexchange.com/questions/1196427/what-does-shear-mean
gansub
CC BY-SA 4.0
2024-11-18T16:36:53.387Z
@gansub if I remember right (I may not), I think shear as an idea is typically calculated meteorologically for current weather use is calculated as just the vector difference in wind, rather than the separate concept of the deformation terms.  Maybe I'm wrong though.  But yeah, that adds an extra complexity as to understanding whether that's what he's interested in.  Certainly seems that terminology is used in too many competing ways (ask a severe weather meteorologist and a pilot what wind shear are, and you'll get plenty of heated debate often)
JeopardyTempest
<meteorology><wind><python>
How to calculate horizontal wind shear (esp. via Python)?
Brian Añano
# How to calculate horizontal wind shear (esp. via Python)?

(Asked by: username_0 on 2024-11-11)

I would like to ask about horizontal wind shear. In most cases, we frequently talk about vertical wind shear (VWS), which is the change in wind speed and direction with height or within a given layer/depth of the atmosphere. I understand that VWS is calculated typically as a vector difference between wind velocities at different levels in the atmosphere, say between the 850 hPa and 200 hPa pressure levels.

What I'm wondering about is: how can I calculate *horizontal* wind shear (HWS)? I'm interested in calculating and visualizing how wind velocities change along the horizontal or parallel to the Earth's surface, preferably via Python given gridded data (esp. reanalysis), especially in phenomena where there are sharp changes in wind velocity (esp. shear lines, but also in true fronts). Since we calculate VWS along an axis (i.e. along the vertical axis), I assume that HWS should also be calculated along an axis, but which axis exactly? Would it be North-South (meridional) or East-West (zonal), or both (like components being combined into a vector)? And how do I calculate the vector differences? Would it be in between points, or in between lines or latitude/longitude?

**Tags:** meteorology, wind, python

> **Comments:**
> **username_1**: Are you asking how to visualize a vector field, or solving an equation to obtain a sheared wind vector field, or do you want real data on wind velocities and obtain your shear from this data? Very unclear question at the moment.  
> **username_2**: I mean you'd calculate it the same way vertical wind shear is calculated... you'd have a horizontal (or pseudo-horizontal if aloft) grid of winds.  You could calculate the difference in vectors between neighboring "x" gridpoints and neighboring "y" gridpoints (and probably diagonally too, to x+1, y+1, to get the fullest field).  I'm sure there are basic functions/packages available to do vector calculations.  
> **username_2**: But I'd think in typical meteorological data, you'll get a horizontal shear that is poorly representative of the values needed for like aviation.  Because the resolution of global and even mesoscale models are quite a few miles/km.  And the biggest issues are much more localized (convective downbursts and such).  For things like planes, or situations that like do damage or such, you need the change over like 100 meters or less.  Whereas the models will be the difference averaged over 3 km or much more.  Plus the coarser gridscale means the peak values will be blurred out in each grid point too  
> **username_2**: Reanalysis is often even worse (I see NCAR has a 2.5° field!  A degree is 111 km/69 miles.  So where you're typically looking for sharp differences over a tiny distance, you're instead only seeing the gradual synoptic differences between states/countries).  If you want an estimate of true potential horizontal shear from reanalysis/global/mesoscale models, I'd believe the only option would be developing analysis equations upon key widescale factors to estimate the possibility of certain shear levels.  Think that's how turbulence, microburst, etc forecasting is typically done regionally.  
> **username_3**: You can take a look at the equation for the horizontal shear here - https://math.stackexchange.com/questions/1196427/what-does-shear-mean  
> **username_2**: @username_3 if I remember right (I may not), I think shear as an idea is typically calculated meteorologically for current weather use is calculated as just the vector difference in wind, rather than the separate concept of the deformation terms.  Maybe I'm wrong though.  But yeah, that adds an extra complexity as to understanding whether that's what he's interested in.  Certainly seems that terminology is used in too many competing ways (ask a severe weather meteorologist and a pilot what wind shear are, and you'll get plenty of heated debate often)  

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## 0 answers

