<p>Cross tropopause transport seems to be the main driver : Take a look at <a href="http://www.climatemonitor.it/wp-content/uploads/2014/04/Kuhl_Tropopause_Folding.ppt" rel="nofollow">this</a>.</p>

CC BY-SA 3.0
2014-05-02T12:50:24.947Z
Can you summarize what is in that presentation that supports your answer as well as develop your answer a bit more than a single sentence?  We like our answers to stand on their own even if that link is someday removed.
casey
CC BY-SA 3.0
2014-05-02T12:33:00.233Z
2014-05-02T12:33:00.233Z
Sean
<p>I am not not an expert in meteorology, but do study the chemistry involved in these types of events.  My understanding is that the folds in the tropopause generally occur below the front of the jet stream, when the potential vorticity is strong enough to transport stratospheric air down through the tropopause/inversion. </p>

<p>Please see the relevant quote from Q. J. R. Meteorol. Soc. (2004), 130, pp. 1195–1212 doi: 10.1256/qj.03.21
Convective mixing in a tropopause fold
By H. J. REID and G. VAUGHAN∗
Institute of Mathematical and Physical Sciences, University of Wales, Aberystwyth, UK</p>

<p><em>"Mixing between stratospheric and tropospheric air can occur most readily in deep
intrusions of stratospheric air into the troposphere, such as tropopause folds (Danielsen
1968). They occur because of the ageostrophic circulation at the jet entrance (Hoskins
1982) and coincide with the frontal zone beneath the jet. Deep folds can extend down to
the top of the boundary layer (Browell et al. 1987; Vaughan et al. 1994), while smaller
folds, extending only into the upper troposphere, are ubiquitous around the polar jet
stream (e.g. Vaughan et al. 2001). They also occur beneath the subtropical jet stream
(Gouget et al. 1996), where it has been suggested that mixing between the subtropical
fold and tropospheric air promotes the generation of new aerosol particles (Zahn et al.
2000). Turbulence within folds can result from shear instability beneath the jet (Pepler
et al. 1998; Hartjenstein 2000) or from convection extending up from the boundary
layer (Browning and Reynolds 1994)."</em></p>

<p>As for synoptic scale weather, I don't think a tropopause fold affects the synoptic scale weather events much, but are rather a part of the weather events.  The downward mixing of stratospheric air will introduce drier air, leading to lower humidity in the general vicinity.  Of course, ozone will be entrained into the tropopause as well, which has air quality implications.  And there are certainly feedbacks in the fold phenomena that will affect heat, radiation, and kinetic patterns... but the synoptic weather in the region is going to be more driven by the jet stream itself rather than a fold that may occur.  A meteorologist, though, might have better information on that.</p>

CC BY-SA 3.0
2014-06-21T04:47:09.040Z
2014-06-25T03:04:48.690Z
2014-06-25T03:04:48.690Z
f.thorpe
<p>What is the process that creates a tropopause fold?  Do these features have any significant impact(s) on weather patterns or the atmosphere?</p>

<p><img src="https://i.sstatic.net/Aolhg.jpg" alt="Cross Section of a Tropopause Fold"></p>

CC BY-SA 3.0
2014-04-17T16:06:11.453Z
This one is on my list to take a crack at once I dust off my graduate synoptic class notes.
casey
<meteorology><troposphere><stratosphere><synoptic><vorticity>
How do tropopause folds form and do they have any impact on synoptic scale weather?
DrewP84
# How do tropopause folds form and do they have any impact on synoptic scale weather?

(Asked by: username_0 on 2014-04-17)

What is the process that creates a tropopause fold? Do these features have any significant impact(s) on weather patterns or the atmosphere?

![Cross Section of a Tropopause Fold](https://i.sstatic.net/Aolhg.jpg)

**Tags:** meteorology, troposphere, stratosphere, synoptic, vorticity

> **Comments:**
> **username_1**: This one is on my list to take a crack at once I dust off my graduate synoptic class notes.  

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## 2 answers

### Answer by username_3 on 2014-06-21. Score: 5 | Accepted answer

I am not not an expert in meteorology, but do study the chemistry involved in these types of events. My understanding is that the folds in the tropopause generally occur below the front of the jet stream, when the potential vorticity is strong enough to transport stratospheric air down through the tropopause/inversion.

Please see the relevant quote from Q. J. R. Meteorol. Soc. (2004), 130, pp. 1195–1212 doi: 10.1256/qj.03.21
Convective mixing in a tropopause fold
By H. J. REID and G. VAUGHAN∗
Institute of Mathematical and Physical Sciences, University of Wales, Aberystwyth, UK

*"Mixing between stratospheric and tropospheric air can occur most readily in deep
intrusions of stratospheric air into the troposphere, such as tropopause folds (Danielsen
1968). They occur because of the ageostrophic circulation at the jet entrance (Hoskins
1982) and coincide with the frontal zone beneath the jet. Deep folds can extend down to
the top of the boundary layer (Browell et al. 1987; Vaughan et al. 1994), while smaller
folds, extending only into the upper troposphere, are ubiquitous around the polar jet
stream (e.g. Vaughan et al. 2001). They also occur beneath the subtropical jet stream
(Gouget et al. 1996), where it has been suggested that mixing between the subtropical
fold and tropospheric air promotes the generation of new aerosol particles (Zahn et al.
2000). Turbulence within folds can result from shear instability beneath the jet (Pepler
et al. 1998; Hartjenstein 2000) or from convection extending up from the boundary
layer (Browning and Reynolds 1994)."*

As for synoptic scale weather, I don't think a tropopause fold affects the synoptic scale weather events much, but are rather a part of the weather events. The downward mixing of stratospheric air will introduce drier air, leading to lower humidity in the general vicinity. Of course, ozone will be entrained into the tropopause as well, which has air quality implications. And there are certainly feedbacks in the fold phenomena that will affect heat, radiation, and kinetic patterns... but the synoptic weather in the region is going to be more driven by the jet stream itself rather than a fold that may occur. A meteorologist, though, might have better information on that.


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### Answer by username_2 on 2014-05-02. Score: -2

Cross tropopause transport seems to be the main driver : Take a look at [this](http://www.climatemonitor.it/wp-content/uploads/2014/04/Kuhl_Tropopause_Folding.ppt).

> **Comments:**
> **username_1**: Can you summarize what is in that presentation that supports your answer as well as develop your answer a bit more than a single sentence?  We like our answers to stand on their own even if that link is someday removed.  

---

