Stratosphere and Polar Vortex Watch

[Blessed Weather]

Dr. Judah Cohen doing some 'thinking out loud' about the polar vortex and various scenarios going forward in his latest weekly update (13 Nov):

"The second item giving me restless nights is the strengthening stratospheric polar vortex.  Currently the troposphere and stratosphere are uncoupled.  The stratospheric PV is predicted to strengthen while the tropospheric circulation at high latitudes is predicted to become increasingly perturbed. The troposphere and stratosphere can remain uncoupled for long periods in the winter but that is often the exception and at some point the stratosphere and troposphere are likely to couple. How the troposphere and stratosphere couple is an open question in my mind. One possibility is that the perturbed or disturbed state of the troposphere is transferred to the stratosphere and then boomerangs back into the troposphere, resulting in a relatively cold winter across the mid-latitudes of the NH. The other possibility is that the mostly zonal circulation associated with the predicted strong stratospheric PV descends from the stratosphere to the troposphere resulting in a relatively mild winter across the mid-latitudes of the NH. Both scenarios seem plausible to me yet the outcomes again would be polar opposite in regards to resultant sensible weather."

Dr. Cohen goes on to outline 3 scenarios going forward, but seems to favour the troposphere and stratosphere coupling in the medium term and a period of more active WAFz or poleward heat transport, leading to an eventual weakening of the strat PV with high level blocking and cold outbreaks into the NH mid-latitudes. He notes this winters' e-QBO could be an influencing factor supporting this scenario.

Note this link goes to the latest blog, so the 13 Nov update will be replaced by the next update in a weeks' time.
http://www.aer.com/science-research/climate-weather/arctic-oscillation

[sebastiaan1973]

http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-16-0259.1

And he refers to this article.

[chionomaniac]

13 minutes ago, Blessed Weather said:

Dr. Judah Cohen doing some 'thinking out loud' about the polar vortex and various scenarios going forward in his latest weekly update (13 Nov):

"The second item giving me restless nights is the strengthening stratospheric polar vortex.  Currently the troposphere and stratosphere are uncoupled.  The stratospheric PV is predicted to strengthen while the tropospheric circulation at high latitudes is predicted to become increasingly perturbed. The troposphere and stratosphere can remain uncoupled for long periods in the winter but that is often the exception and at some point the stratosphere and troposphere are likely to couple. How the troposphere and stratosphere couple is an open question in my mind. One possibility is that the perturbed or disturbed state of the troposphere is transferred to the stratosphere and then boomerangs back into the troposphere, resulting in a relatively cold winter across the mid-latitudes of the NH. The other possibility is that the mostly zonal circulation associated with the predicted strong stratospheric PV descends from the stratosphere to the troposphere resulting in a relatively mild winter across the mid-latitudes of the NH. Both scenarios seem plausible to me yet the outcomes again would be polar opposite in regards to resultant sensible weather."

Dr. Cohen goes on to outline 3 scenarios going forward, but seems to favour the troposphere and stratosphere coupling in the medium term and a period of more active WAFz or poleward heat transport, leading to an eventual weakening of the strat PV with high level blocking and cold outbreaks into the NH mid-latitudes. He notes this winters' e-QBO could be an influencing factor supporting this scenario.

Note this link goes to the latest blog, so the 13 Nov update will be replaced by the next update in a weeks' time.
http://www.aer.com/science-research/climate-weather/arctic-oscillation

I'm no scientist, but the coupling of trop and strat is my favoured option. We need to keep an eye on the upper strat u wind mean speeds and watch these descend. I suspect it gives us a limited time to prosper from any trop disturbances before the risk of zonality returns.

[Summer Sun]

 

 

Edited November 14, 2017 by Summer Sun

[Singularity]

Given the above points from various contributors, a vortex versus amplified planetary waves period seems the best to hope for. Question is, will there be a decent tropical perturbation to work with? A high-stakes game for those attempting to produce guidance for the season ahead.

[comet]

Seems to me that Mr Cohen does not have a Scooby do about what may happen or may not happen. So much for a -QBO = weak vortex, this may be due though to the fact that it has been allowed to build unaffected in the mid to upper strat because of the disconnect and little if any wave breaking in the upper strat.

I think I am correct in saying that the infamous cold spell of Jan 87 was the result of a decoupled trop and strap with little in if any signature of raised heights or warming above 50 or even 100mb.

[Catacol]

1 hour ago, Singularity said:

Given the above points from various contributors, a vortex versus amplified planetary waves period seems the best to hope for. Question is, will there be a decent tropical perturbation to work with? A high-stakes game for those attempting to produce guidance for the season ahead.

I think you are spot on here. Much will depend on the next MJO cycle late Dec and the extent to which Nina has taken hold. By late December it seems likely the current strat/trop disconnect will have ended with westerlies descending from the upper strat and taking hold (no signs of an early season warming at this stage) and unless something changes soon a zonal December looks increasingly likely. If we don’t get decent tropical forcing from the next cycle then High lat blocking will be hard to sustain. 

But these remain ifs and buts at this stage. Long way to go. As we saw last year early building blocks and supposition based on November conditions can soon turn around. Cohen implied as much yesterday and plenty of other experts across the Twitter sphere are hedging their bets at this stage.

Anyone heard from GP recently? I know he cannot give away too much these days, but his interpretation of conditions over the next 3-4 weeks would be interesting and valuable.

[chionomaniac]

3 hours ago, comet said:

Seems to me that Mr Cohen does not have a Scooby do about what may happen or may not happen. So much for a -QBO = weak vortex, this may be due though to the fact that it has been allowed to build unaffected in the mid to upper strat because of the disconnect and little if any wave breaking in the upper strat.

I think I am correct in saying that the infamous cold spell of Jan 87 was the result of a decoupled trop and strap with little in if any signature of raised heights or warming above 50 or even 100mb.

Cough... This statement couldn't be more untrue, lol. SSW late Dec 86 leading to this:

[comet]

36 minutes ago, chionomaniac said:

Cough... This statement couldn't be more untrue, lol. SSW late Dec 86 leading to this:

I have seen this before but there is no trace of it in the lower strat when you look on the ESRL daily mean composites charts above 100mb. Just realised I should of been looking at the anomaly charts rather than the mean. Good to see that the records back each other up. I had been dubious of the ESRL charts for a while now because of this. Cheers.

[lorenzo]

https://www.esrl.noaa.gov/csd/groups/csd8/sswcompendium/

 

worth a repost re reanalysis..

[Interitus]

9 hours ago, chionomaniac said:

Cough... This statement couldn't be more untrue, lol. SSW late Dec 86 leading to this:

SSW was 23rd Jan 1987 - after the severest cold of that month

[JeffC]

Possibly naive question to the more learned members, which area potentially holds more sway? Air will be denser in the troposphere and therefore can that influence the stratosphere more, or because the air is colder in the stratosphere does that knock the troposphere more.

I suppose what I'm asking is can a disorganised trop PV knock an organized strat pv out of kilter like a form of SSW, or does the organised strat pv always result in an organised trop pv if they couple up?

Ta

[knocker]

6 minutes ago, JeffC said:

Possibly naive question to the more learned members, which area potentially holds more sway? Air will be denser in the troposphere and therefore can that influence the stratosphere more, or because the air is colder in the stratosphere does that knock the troposphere more.

I suppose what I'm asking is can a disorganised trop PV knock an organized strat pv out of kilter like a form of SSW, or does the organised strat pv always result in an organised trop pv if they couple up?

Ta

This is not a direct answer to your question, I don't pretend to be very knowledgeable vis the Strat, but if you, and others, haven't read it this article is worth a read (it's quite likely to have been posted in here already of course)

What Is the Polar Vortex and How Does It Influence Weather?

http://journals.ametsoc.org/doi/full/10.1175/BAMS-D-15-00212.1

[JeffC]

18 minutes ago, knocker said:

This is not a direct answer to your question, I don't pretend to be very knowledgeable vis the Strat, but if you, and others, haven't read it this article is worth a read (it's quite likely to have been posted in here already of course)

What Is the Polar Vortex and How Does It Influence Weather?

http://journals.ametsoc.org/doi/full/10.1175/BAMS-D-15-00212.1

Thanks Knocker, one to read when the hours of wage slavery have passed!

[Blessed Weather]

I'd be grateful if one of the strat experts on here could check my interpretation of the JMA Zonal Mean Zonal Wind latitude-height chart please. My take:

• the zonal winds at 10 hPa 60N are westerly and slowly ticking up (yesterday 33.6 m/s, today 34.7 m/s) and that the stronger winds are slowly descending down through the strat.
• the winds at 30 hPa over the equator are easterly and thus show an e-QBO.

And finally, what is causing the burst of stronger westerlies at 300 hPa 30N? I don't understand that one! Thanks in anticipation.

[chionomaniac]

5 minutes ago, Blessed Weather said:

I'd be grateful if one of the strat experts on here could check my interpretation of the JMA Zonal Mean Zonal Wind latitude-height chart please. My take:

• the zonal winds at 10 hPa 60N are westerly and slowly ticking up (yesterday 33.6 m/s, today 34.7 m/s) and that the stronger winds are slowly descending down through the strat.
• the winds at 30 hPa over the equator are easterly and thus show an e-QBO.

And finally, what is causing the burst of stronger westerlies at 300 hPa 30N? I don't understand that one! Thanks in anticipation.

Just quickly - you are right in your interpretation  so that is good . The stronger westerlies at 300hPA are reflective of the southerly displaced jet stream - we are in the troposphere at that point!

[Walsall Wood Snow]

3 hours ago, Interitus said:

SSW was 23rd Jan 1987 - after the severest cold of that month

This is a good point I think, as I've also heard that an SSW can in fact knock us out of a cold spell as well as make one a greater possibility?

[karyo]

42 minutes ago, Walsall Wood Snow said:

This is a good point I think, as I've also heard that an SSW can in fact knock us out of a cold spell as well as make one a greater possibility?

Indeed! That's what happened in winter 2008/9. We had a reasonably cold and wintry winter until the SSW changed the pattern and gave us a mild Feb and March.

[knocker]

2 hours ago, chionomaniac said:

Just quickly - you are right in your interpretation  so that is good . The stronger westerlies at 300hPA are reflective of the southerly displaced jet stream - we are in the troposphere at that point!

Just to clarify a point chio when you say reflective of the southerly displaced jet stream are you talking of the Subtropical jet because 30n is just about where it sits or the Polar jet a long way south?

Diagram courtesy Atmosphere, Weather & Climate by Barry and Chorley

 

Edited November 15, 2017 by knocker

[bluearmy]

2 hours ago, Blessed Weather said:

I'd be grateful if one of the strat experts on here could check my interpretation of the JMA Zonal Mean Zonal Wind latitude-height chart please. My take:

• the zonal winds at 10 hPa 60N are westerly and slowly ticking up (yesterday 33.6 m/s, today 34.7 m/s) and that the stronger winds are slowly descending down through the strat.
• the winds at 30 hPa over the equator are easterly and thus show an e-QBO.

And finally, what is causing the burst of stronger westerlies at 300 hPa 30N? I don't understand that one! Thanks in anticipation.

Looking at the Berlin charts from yesterday’s op, the zonal winds are descending over the next few days towards 50 hpa but then begin to pull back somewhat. 

[MP-R]

3 hours ago, karyo said:

Indeed! That's what happened in winter 2008/9. We had a reasonably cold and wintry winter until the SSW changed the pattern and gave us a mild Feb and March.

Pretty sure it was the SSW that brought about the Feb cold spell??

[Walsall Wood Snow]

1 minute ago, MP-R said:

Pretty sure it was the SSW that brought about the Feb cold spell??

Mods please delete this post. Quoted by mistake.

[Interitus]

3 hours ago, knocker said:

Just to clarify a point chio when you say reflective of the southerly displaced jet stream are you talking of the Subtropical jet because 30n is just about where it sits or the Polar jet a long way south?

Diagram courtesy Atmosphere, Weather & Climate by Barry and Chorley

 

Correct, it is the subtropical jet - the chart posted by Blessed Weather shows the polar jet at 60°N from 8-10th Nov, but then vanishes on 11-13th Nov as it becomes more meridional so the zonal mean westerlies diminish.

Of course jet stream names are often slightly arbitrary, based on mean latitude, when it spirals northwards over the Atlantic - so a 30°N STJ over the southern US can become a 60° PJ north of the UK

[sebastiaan1973]

Abstract

A Northern Hemisphere (NH) polar stratospheric pathway for La Niña events is established during wintertime based on reanalysis data for the 1958–2012 period. A robust polar stratospheric response is observed in the NH during strong La Niña events, characterized by a significantly stronger and cooler polar vortex. Significant wind anomalies reach the surface, and a robust impact on the North Atlantic–European (NAE) region is observed. A dynamical analysis reveals that the stronger polar stratospheric winds during La Niña winters are due to reduced upward planetary wave activity into the stratosphere. This finding is the result of destructive interference between the climatological and the anomalous La Niña tropospheric stationary eddies over the Pacific–North American region.

In addition, the lack of a robust stratospheric signature during La Niña winters reported in previous studies is investigated. It is found that this is related to the lower threshold used to detect the events, which signature is consequently more prone to be obscured by the influence of other sources of variability. In particular, the occurrence of stratospheric sudden warmings (SSWs), partly linked to the phase of the quasi-biennial oscillation, modulates the observed stratospheric signal. In the case of La Niña winters defined by a lower threshold, a robust stratospheric cooling is found only in the absence of SSWs. Therefore, these results highlight the importance of using a relatively restrictive threshold to define La Niña events in order to obtain a robust surface response in the NAE region through the stratosphere.

The Stratospheric Pathway of La Niña

Maddalen Iza and Natalia CalvoDepartamento de Física de la Tierra II, Universidad Complutense de Madrid, Madrid, Spain
Elisa ManziniMax Planck Institute for Meteorology, Hamburg, Germany

[Snowy Hibbo]

12 hours ago, Blessed Weather said:

I'd be grateful if one of the strat experts on here could check my interpretation of the JMA Zonal Mean Zonal Wind latitude-height chart please. My take:

• the zonal winds at 10 hPa 60N are westerly and slowly ticking up (yesterday 33.6 m/s, today 34.7 m/s) and that the stronger winds are slowly descending down through the strat.
• the winds at 30 hPa over the equator are easterly and thus show an e-QBO.

And finally, what is causing the burst of stronger westerlies at 300 hPa 30N? I don't understand that one! Thanks in anticipation.

This graphic of the whole atmosphere both NH and SH may help. The SH shows the two jetstreams better than the NH ATM.

The NH Polar Jet, as already mentioned, is weak with the current -AO setup. I use these charts frequently to check up on the jetstreams, along with the QBO...

Edited November 15, 2017 by Snowy Hibbo