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Stratosphere Temperature Watch 2012/2013

stratosphere qbo bdc ssw mmw

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#1 chionomaniac

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Posted 30 September 2012 - 00:42

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Welcome to the new season stratosphere thread for the 2012/2013 stratospheric NH winter.

With the excitement building and expectations high for the coming winter, the role of the polar stratosphere will play an important part in determining what type of winter we shall have.

As ever for those new to the stratospheric input I will include in this post a basic guide to how the stratosphere may influence tropospherical weather systems before looking at what we can expect this winter.

The stratosphere is the layer of the atmosphere situated between 10km and 50km above the earth. It is situated directly above the troposphere, the first layer of the atmosphere that is directly responsible for the weather that we receive. The boundary between the stratosphere and the troposphere is known as the tropopause. The air pressure ranges from around 100hPa at the lower levels of the stratosphere to around 1hPa at the upper levels. The middle stratosphere is often considered to be around the 30hPa level.

Every winter the stratosphere cools down dramatically as less solar UV radiation is absorbed by the ozone content in the stratosphere. The difference in the temperature between the North Pole and the latitudes further south creates a strong vortex – the wintertime stratospheric polar vortex. The colder the stratosphere, the stronger this vortex becomes. The stratospheric vortex has a strong relationship with the tropospheric vortex below. The stronger the stratospheric vortex, the stronger the tropospheric vortex becomes.

The strength and position of the tropospheric vortex influences the type of weather that we are likely to experience. A strong polar vortex is more likely to herald a positive AO with the resultant jet stream track bringing warmer wet southwesterly winds. A weaker polar vortex can contribute to a negative AO with the resultant mild wet weather tracking further south.

Posted Image

The stratosphere is a far more stable environment then the troposphere below it. However, there are certain influences that can bring about changes - the stratospheric ozone content, the phase of the solar cycle, the Quasi Biennial Oscillation ( the QBO), wave breaking events from the troposphere and the autumnal Eurasion/Siberian snow cover to name but a few.

The ozone content in the polar stratosphere has been shown to be destroyed by CFC's permeating to the stratosphere from the troposphere but there can be other influences as well. Ozone is important because it absorbs UV radiation which creates warming of the stratosphere. The Ozone is formed in the tropical stratosphere and transported to the polar stratosphere by a system known as the Brewer-Dobson -Circulation. The strength of this circulation varies from year to year and can in turn be dictated by other influences.

One of these influences is the QBO. This is a tropical stratospheric wind that descends in an easterly then westerly direction over a period of around 28 months. This can have a direct influence on the strength of the polar vortex in itself. The easterly (negative ) phase is though to contribute to a weakening of the stratospheric polar vortex, whilst a westerly (positive) phase is thought to increase the strength of the stratospheric vortex. However, in reality the exact timing and positioning of the QBO is not precise and the timing of the descending wave is critical throughout the winter.

The direction of the QBO when combined with the level of solar flux has been shown to influence the BDC. When the QBO is in a west phase during solar maximum there are more warming events (increased strength BDC) in the stratosphere as there is during an easterly phase QBO during solar minimum. ( http://strat-www.met...-et-al-2006.pdf )

The QBO is measured at 30 hPa and has been in an easterly phase since August 2011 (http://www.esrl.noaa...lation/qbo.data). The easterly phase is likely to come to an end at 30 hPa over the coming winter, however, even after this we are likely to see easterly winds descend the stratosphere spreading polewards for some time yet.

The easterly QBO winds can be demonstrated on the following zonal wind stratospheric profile chart:

ecmwfzm_u_a12-1.gif



One warming event that can occur in the stratospheric winter is a Sudden Stratospheric Warming ( SSW) or also known as a Major Midwinter Warming (MMW). This as the name suggests a rather dramatic event. Normally the polar night jet at the boundary of the polar vortex demarcates the boundary between warmer tropical and cooler polar stratospheric air (and ozone levels) and is very difficult to penetrate. SSWs can be caused by large-scale planetary waves being deflected up into the stratosphere and towards the North Pole, often after a strong mountain torque event. These waves can introduce warmer temperatures into the polar stratosphere and can seriously disrupt the stratospheric vortex, leading to a slowing or even reversal of the vortex. This can occur by the vortex being displaced off the pole – a displacement SSW, or by the vortex being split in two – a splitting SSW.

The effects of a SSW can be transmitted into the troposphere as the propagation of the SSW occurs and this can have a number of consequences. There is a higher incidence of northern blocking after SSW’s but we are all aware that not every SSW leads to northern blocking. Any northern blocking can lead to cold air from the tropospheric Arctic flooding south and colder conditions to latitudes further south can ensue. There is often thought to be a time lag between a SSW and northern blocking from any downward propagation of negative mean zonal winds from the stratosphere. This has been quoted as up to 6 weeks though it can be a lot quicker if the polar vortex is ripped in two following a split SSW.

One noticeable aspect of the recent previous winters is how the stratosphere has been susceptible to wave breaking from the troposphere through the lower reaches of the polar stratosphere - not over the top as seen in the SSWs. This has led to periods of sustained tropospheric high latitude blocking and repeated lower disruption of the stratospheric polar vortex. This has coincided with a warmer stratosphere where the mean zonal winds have been reduced and has led to some of the most potent winter spells witnessed in recent years.

So the question to be asked is are we able to predict how the stratosphere is likely to behave this year. The real answer is not yet, though there are some aspects that we can use as a guide looking at previous years.

The most useful of these is the easterly descending QBO. We know that the stratospheric polar vortex is a lot weaker in easterly years and more susceptible to disruption. Combine this with what is in effect a low solar maximum then this may enhance this effect. See post from GP in last thread regarding analogue year 1968-69

I have been collecting relavent papers regarding the role of the stratosphere and other influences and they can be found here - http://forum.netweat...nective-papers/

I am starting this thread earlier than normal because of the increased importance that has been placed on the role of the stratosphere since I first monitored a few years back. Rather than being viewed as a small piece in the jigsaw, it is being realised that the state of the stratosphere can/may overrule all other teleconnective pieces. Last years cold stratosphere demonstrated this only too well.

So it is eyes down (or up!) in the coming weeks to monitor how the polar stratosphere cools and what affect this has on the strength of the stratospheric polar vortex.

There are a number of sites that provide information regarding this.

Firstly, the two important sites that can be used to look at the temperature profiles are:

http://acdb-ext.gsfc...t/ann_data.html

and

http://www.cpc.ncep....re/temperature/

Graphically and previous years information :

http://www.cpc.ncep....ere/strat-trop/

and

http://www.geo.fu-be...pole/index.html

Forecasts:

http://wekuw.met.fu-.../wdiag/diag.php

and

http://www.cpc.ncep....here/strat_a_f/

and not forgetting!

http://www.netweathe...atosphere;sess= (more available on nw extra!)


So, as ever, we have a lot to keep an eye on. Early indications suggest that the polar stratosphere is cooling pretty much as expected. I am happy to report that there are already signs that this cooling is not uniform, with a Canadian warming a possibility this autumn. It's early days to see a slightly warmer area, but the GFS forecast does suggest this-

gfs_t30_nh_f240.gif

An early heartener!

Happy strat watching fellow strat watchers!

c
  • 42

Not long to go before the new strat thread appears........ Winter must be coming. Its here! - http://forum.netweat...4/#entry2806873

 

Links to previous strat threads - http://forum.netweat...80#entry2445171

Burgess Hill.


#2 lorenzo

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Posted 30 September 2012 - 01:37

First Class C.
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#3 johnholmes

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Posted 30 September 2012 - 07:24

Thanks C plenty of information for everyone to try and get up to speed and your posts will be eagerly looked for by the coldies on here=most folk.
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#4 Rollo

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Posted 30 September 2012 - 08:01

Excellent review C and so beautifully explained- even my understanding is increased.
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#5 phil nw.

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Posted 30 September 2012 - 08:02

Good opening post Ed- very informative. Many of us have looked forward to this thread and i am sure it will be one of the most visited this Winter.
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Phil nw.

 

Veteran of the 1962/63 Winter when Snow lay for 66 days ---will we ever see its like again?.

 

 


#6 Cloud 10

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Posted 30 September 2012 - 09:42

Always nice to see the new strat thread opened,and a great introductory post by Chio. Posted Image



An interesting post by GP in the old thread (GP copy into this thread?) showing
how the stratosphere might behave this winter by using 1968 as an analogue.

The 30mb zonal wind composite for the winter of 68/69 shows the reduction in
zonal winds at mid-latitudes very nicely...

zonal winds 30mb.gif


....along with the sea level pressure anomalies. Posted Image

compday.91.135.10.220.273.3.15.2.gif
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Winter 2013/14 Dec-Feb

Frosts 26

Days snow fell 9

 

 


#7 Mrs Trellis

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Posted 30 September 2012 - 10:07

Many thanks for that, Ed...After years' of 'ignoring' acronyms, some have finally stuck!
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#8 syed2878

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Posted 30 September 2012 - 12:24

good to c the strat thread reopening again nice explanation chio.
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UP WITH THE VILLA, AND DOWN WITH THE BLUES!!!...

#9 MattHugo

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Posted 30 September 2012 - 12:35

Stratospheric analysis and discussion at 1:40am on a Sunday morning...Now that's dedication, or perhaps insomnia Posted Image

Good to see the thread open, here's to the coming weeks and months and lets hope we aren't looking back on this come next March with disappointment. Clearly I am speaking from a person who is also after/favours a more blocked pattern this winter, particularly given the summer we have had. A winter period dominated by zonal, mild, wet and windy muck is not wanted IMO.

Regards to all,

M.
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#10 gottolovethisweather

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Posted 01 October 2012 - 10:22

I hope Matt doesn't mind, but this is hot off the press and I'm sure it is well worth a read. Posted ImageTime for a strong coffee, there is some learning to be done.

http://matthugo.word...is-information/
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Formally STORMBOY, come visit my Blog http://naturestimeline.com/ to learn more about this slightly eccentric anorak, who goes by the name of Tony!

Finally, two quotes from two very different recent Winters.

"Wasn't it enough that we lived through the coldest December for over 100 years that no one alive has experienced?" and "Wasn't it enough that we lived through the wettest December - February for over 250 years that no one alive has experienced?"


#11 Mark N

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Posted 01 October 2012 - 10:49

I hope Matt doesn't mind, but this is hot off the press and I'm sure it is well worth a read. Posted ImageTime for a strong coffee, there is some learning to be done.

http://matthugo.word...is-information/


Fantastic blog post by Matt Posted Image , i now know alot more than i did 10-15 minutes ago. Thanks for sharing GTLTW.
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**Location- Headington,Oxfordshire (115m)**

Winter 2013/14
Frosts- 10
Lowest Temperature:- -3.3c December 3rd.
Snow falling/lying = 0/0 days

#12 chionomaniac

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Posted 01 October 2012 - 11:27

I hope Matt doesn't mind, but this is hot off the press and I'm sure it is well worth a read. Posted ImageTime for a strong coffee, there is some learning to be done.

http://matthugo.word...is-information/


It's great to get the word out there in a clear concise way - I've been trying long enough but without Matt's profile.

Technically, last January there wasn't a SSW as defined by Polvani et al (winds reversal at 60ºN and 10hPa), but I can let Matt off as the result in this case is pretty much the same as if there had been!
  • 0

Not long to go before the new strat thread appears........ Winter must be coming. Its here! - http://forum.netweat...4/#entry2806873

 

Links to previous strat threads - http://forum.netweat...80#entry2445171

Burgess Hill.


#13 chionomaniac

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Posted 01 October 2012 - 11:39

Todays update; The stratosphere is currently cooling rapidly as is expected at this time of year. Last week we saw a blip where the mean zonal winds went below average for this time of year in the lower stratosphere. These have since recovered and are or about to increase to above average. Encouragingly, the cooling of the polar stratosphere is not forecast to be straightforward with small projected warmings forecast over the Canadian sector which will put pressure on the strengthening vortex. All of this has been in stratospheric FI but the theme has remained the same, with a lower split even cropping up. Very much a trend that we want to see continue into winter!
  • 4

Not long to go before the new strat thread appears........ Winter must be coming. Its here! - http://forum.netweat...4/#entry2806873

 

Links to previous strat threads - http://forum.netweat...80#entry2445171

Burgess Hill.


#14 bluearmy

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Posted 01 October 2012 - 12:47

Todays update;

The stratosphere is currently cooling rapidly as is expected at this time of year.

Last week we saw a blip where the mean zonal winds went below average for this time of year in the lower stratosphere. These have since recovered and are or about to increase to above average.

Encouragingly, the cooling of the polar stratosphere is not forecast to be straightforward with small projected warmings forecast over the Canadian sector which will put pressure on the strengthening vortex. All of this has been in stratospheric FI but the theme has remained the same, with a lower split even cropping up. Very much a trend that we want to see continue into winter!


ed, do you think interruptions to the rate of cooling are more important than the actual temp that the strat eventually ends up come november re a strong organised early winter vortex ?
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#15 chionomaniac

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Posted 01 October 2012 - 12:52

Nick, I think that the interruptions may help prevent the straightforward cooling of the strat, so are important in both senses. If at the end of November we have a strong vortex in a cold strat then obviously they may not have helped as much as I anticipate!
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Not long to go before the new strat thread appears........ Winter must be coming. Its here! - http://forum.netweat...4/#entry2806873

 

Links to previous strat threads - http://forum.netweat...80#entry2445171

Burgess Hill.


#16 22nov10blast

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Posted 01 October 2012 - 18:10

Excellent, really looking forward to this thread! It was too technical for me last year but I will have a better grip this year as my knowledge has improved greatly since then. Thanks to Chionomaniac and all those who will contribute to this thread through the Autumn and Winter. It will be brilliant reading!

Edited by 22nov10blast, 01 October 2012 - 18:10 .

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#17 kumquat

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Posted 03 October 2012 - 02:03

Looking forwards to your posts Chiono. A great introductory post. Can you explain a little more about the phenomenon of "wave-breaking" as in this quote "One noticeable aspect of the recent previous winters is how the stratosphere has been susceptible to wave breaking from the troposphere through the lower reaches of the polar stratosphere - not over the top as seen in the SSWs"

What is the cause of "wave breaking"? What are the outside influences on sudden stratospheric "warming" events? Are we talking about sun activity? Does this depend on sun activity cycles / sunspots?

Always wanting to learn more :) - thanks for the insights.
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#18 chionomaniac

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Posted 03 October 2012 - 18:44

Looking forwards to your posts Chiono. A great introductory post. Can you explain a little more about the phenomenon of "wave-breaking" as in this quote "One noticeable aspect of the recent previous winters is how the stratosphere has been susceptible to wave breaking from the troposphere through the lower reaches of the polar stratosphere - not over the top as seen in the SSWs"

What is the cause of "wave breaking"? What are the outside influences on sudden stratospheric "warming" events? Are we talking about sun activity? Does this depend on sun activity cycles / sunspots?

Always wanting to learn more Posted Image - thanks for the insights.


Hi kumquat.

Lots of questions and ones that took me a lot of time to get my head around.

The tropospheric atmosphere consists of large scale planetary waves that flow from west to east normally. These waves are known as Rossby waves and there can be a number of these flowing around the NH at any one time. As with any wave there is a peak and a trough between . I have demonstrated the troughs in the following NH H500 ECM chart (typically not an easy day to demonstrate!)

Recmnh241.gif

The height of the atmosphere varies between the peaks and the troughs of these waves and as a wave comes in from the sea and break as it nears land the same phenomenem can occur with Rossby waves. However, these waves need to be a certain amplitude before this occurs and need to hit a large planetary object such as a mountain range before this occurs.

So when a large Rossby wave hits a mountain range (like a ripple from a pebble) we can see this wave break upwards into the stratosphere (as well as be deflected sideways into the troposphere and lose energy to the earth in the form of a mountain torque). The effect of a wave breaking into the stratosphere will depend upon the size of the wave - the bigger the wave, the greater the deflection. Once a wave is big enough it can create a disturbance which travels around the boundary of the stratospheric polar vortex - known as the 'surf zone' - and penetrate into the polar vortex at the top of the stratosphere. It can then rebound back towards the troposphere and if it is great enough completely disrupt the polar vortex causing it to warm as it does so. Hence a Sudden Stratospheric Warming (SSW).

These type of wave breaks occur regularly but are of insufficient strength to create SSW's most of the time. If one wave breaks into the stratosphere at any one time we have a wavenumber 1 type break, if two occur simultaneously then we have a wavenumber 2 type and so on.

One other thing to note is that I have witnessed similar type breaks into the stratosphere in recent years that have occurred with planetary waves breaking around Greenland. Rather than travelling up around the surf zone to the top of the stratosphere these wave break 'internally' - almost through the core of the vortex. It is these types of break that do not create full SSWs but have led to very potent cold outbreaks here in recent years.

If in the following link you click ' ongoing observations' and then 'Rossby waves shed by greenland' it is easier to visualise how these interactions occur.

http://www.pa.op.dlr...ctic/index.html

Ps if any one can embed this into a post I would be grateful!

c

Edited by chionomaniac, 03 October 2012 - 20:37 .

  • 3

Not long to go before the new strat thread appears........ Winter must be coming. Its here! - http://forum.netweat...4/#entry2806873

 

Links to previous strat threads - http://forum.netweat...80#entry2445171

Burgess Hill.


#19 phil nw.

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Posted 03 October 2012 - 19:46

Thanks for that Ed-i wondered what the difference between Wavenumber 1 and 2 actually meant. From your explanation that a Wavenumber 2 event is a double event am i correct in assuming that this would give a better chance of an effective SSW.?
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Phil nw.

 

Veteran of the 1962/63 Winter when Snow lay for 66 days ---will we ever see its like again?.

 

 


#20 chionomaniac

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Posted 03 October 2012 - 19:50

Thanks for that Ed-i wondered what the difference between Wavenumber 1 and 2 actually meant.
From your explanation that a Wavenumber 2 event is a double event am i correct in assuming that this would give a better chance of an effective SSW.?


It's a certain wavelength pattern breaking into the stratosphere commonly with Atlantic and Pacific wave breaks. Wavenumber 2 breaks are more likely to cause split SSWs rather than wavenumber 1 breaks which are the cause of displacement SSWs.

Edited by chionomaniac, 03 October 2012 - 19:51 .

  • 2

Not long to go before the new strat thread appears........ Winter must be coming. Its here! - http://forum.netweat...4/#entry2806873

 

Links to previous strat threads - http://forum.netweat...80#entry2445171

Burgess Hill.






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