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Stratosphere Temperature Watch 2011/2012

stratosphere qbo mean zonal mean wind 10hpa 30hpa 100 hpa tropopause polar vortex polar night jet

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#1 chionomaniac

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Posted 24 October 2011 - 14:01

Welcome to the new season stratosphere temperature watch for the upcoming winter.

Once again we shall be looking at the polar stratosphere this coming season, to help give us guidance to how this may influence tropospheric conditions. As always a brief description of why this is important is provided below.

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.

arctic_oscillation.jpg

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. One such influences is the ozone transport mechanism from the tropical stratosphere to the polar stratosphere, known as the Brewer Dobson Circulation (BDC). 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 )

This winter we are around the mid solar cycle and easterly QBO in the mid stratosphere - I think it is difficult to draw any firm conclusions from this.

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.

Here are a list of sites for data on the latest state of the stratosphere:

http://www.columbia....Volume-2010.pdf


Other essential sites

CPC- http://www.cpc.ncep....s/stratosphere/

ECM (from 1/11 hopefully) - http://wekuw.met.fu-.../wdiag/diag.php

JMA - http://ds.data.jma.g...x.html#monit_nh

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

The sudden stratospheric warming site - http://www.appmath.c.../ssws/index.php




So that brings us neatly on to conditions so far for this year.

Recently we have seen a period of decreased mean zonal winds at 30 hPa but this is now changing:

http://acdb-ext.gsfc..._2011_merra.pdf

A cooling of the stratosphere is currently occurring with no forecast warming and ozone forecasts look low. So I would expect an increase in both the stratospheric and tropospheric polar vortices with no major blocking to occur from stratospheric influences for the next four weeks.

For the rest of winter, hopefully the stratosphere will gives us an early warning, but a SSW in January and a cold February is what I would be looking out for... we can but hope.

c

Edited by chionomaniac, 24 October 2011 - 16:50 .

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 knocker

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Posted 24 October 2011 - 14:15

Thanks for that excellent post Chio. As usual very informative. Regarding the QBO I'm still trying to get my head around this paper. I think it's a case of running before walking and as for the Eliassen-Palm Flux..........................

http://citeseerx.ist...p=rep1&type=pdf

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#3 chionomaniac

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Posted 24 October 2011 - 14:52

Thanks for that excellent post Chio. As usual very informative. Regarding the QBO I'm still trying to get my head around this paper. I think it's a case of running before walking and as for the Eliassen-Palm Flux..........................

http://citeseerx.ist...p=rep1&type=pdf

Thanks ws. I have always said that the effects of the QBO on the polar stratosphere are complex and I think at quick glance that paper proves it. However, it looks a good read to a dullard like me!


Here is a cross section of the current mean zonal wind anomalies and I have marked the remnants of the west QBO and main east QBO which hopefully can be put against the paper that you have provided.


ecmwfzm_u_a12.gif

Hopefully, by the end of this season, I will have a better understanding of the EP flux, in such a way that I will be able to demonstrate how wave breaking events affect the stratosphere.

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.


#4 Terminal Moraine

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Posted 24 October 2011 - 15:29

What an excellent post, Chino. I look with envy at people such as yourself and G.P as my ageing brain struggles to come to terms with all the complex interactions of the different circulations, torque events etc etc.
I might get there one day and posts like yours can only help.
Patiently awaiting the return of the Younger Dryas.

#5 chionomaniac

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Posted 24 October 2011 - 15:31

What an excellent post, Chino. I look with envy at people such as yourself and G.P as my ageing brain struggles to come to terms with all the complex interactions of the different circulations, torque events etc etc.
I might get there one day and posts like yours can only help.

Thanks TM,

I have to say in return I envy your meticulous record keeping!!

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.


#6 Radiating Dendrite

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Posted 24 October 2011 - 15:54

I don't know about the stratosphere hotting up, but it is certainly hotting up between TM and CM! Posted Image

#7 sebastiaan1973

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Posted 24 October 2011 - 16:03

This might be an interesting read
http://www.usmessage...009-2010-a.html

Ain't it true that La NIna leads to a colder stratopshere?

Edited by sebastiaan1973, 24 October 2011 - 16:08 .


#8 Isolated Frost

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Posted 24 October 2011 - 16:10

Lol RD!!

Absolutely brill post chiono; I have a much better understanding now :)

November @ Durham University (to the 8th)
9.3° (-0.1°) | 1.7° (-1.7°)|5.5° (-0.9°) | 11.6° (1st) | -1° (1st/4th)

#9 karyo

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Posted 24 October 2011 - 16:14

This might be an interesting read
http://www.usmessage...009-2010-a.html

Ain't it true that La NIna leads to a colder stratopshere?


It certainly did last year!

Karyo

#10 syed2878

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Posted 24 October 2011 - 16:22


Hey an excelent post i must say i've learned quite alot. Thanks.
UP WITH THE VILLA, AND DOWN WITH THE BLUES!!!...

#11 chionomaniac

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Posted 24 October 2011 - 17:00

I don't know about the stratosphere hotting up, but it is certainly hotting up between TM and CM! Posted Image


That made me laugh out loud!!

This might be an interesting read
http://www.usmessage...009-2010-a.html

Ain't it true that La NIna leads to a colder stratopshere?


Not necessarily during an easterly QBO. That is what makes this year so difficult to call stratospherically.

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.


#12 minus 9

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Posted 24 October 2011 - 17:34

Great post chio. Great for people like me. Learning all the time. Thanks.

#13 phil nw.

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Posted 24 October 2011 - 18:32

Thanks from me too Chino.

I always look at your postings and like others appreciate the clear way you explain things.

Keep up the good work.

Phil nw.

 

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

 

 


#14 feb1991blizzard

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Posted 24 October 2011 - 20:34

Thanks chiono for the time and effort you put into keeping us updated.

#15 damianslaw

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Posted 24 October 2011 - 20:55

A very good read and mostly easy to follow. I now understand where Mountain torque events fit into the picture - even though I don't actually know what they mean. Another term often used in the techincal thread is the MJO phase - I note this term isn't used in your post - so I'm still none the wiser what this particular term means.

I'd be interested to know how the stratosphere behaved this time last year and whether it was an influence on conditions late in Nov and through December. I do seem to remember it wasn't exactly favourable for the cold conditions we saw. I also remembered how in Feb 2009 the SSW event though intially delivered the goods on the snow and cold stakes thus quickly prevented any further cold and snowy set ups and the second half of Feb was a major dissapointment depsite the very favourable state of the stratosphere. The state of the stratosphere is thus only one influencing factor for prospects for cold and snow, it isn't the be all and end all.

#16 lorenzo

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Posted 24 October 2011 - 21:22

Excellent post Chiono - I think the Free university of Berlin site is updating already for this season.

Looking forward to the forecasts as they really did lead the models last winter, especially where PV Splits evolved.

Netweather Extra       Regional Discussion     Severe Weather     Stratosphere 2013/14        Technical Research         Winter 2013/14

 

My own weather Blog     http://scotlandwx.co.uk/   Updated with a ton of useful links

 

 


#17 chionomaniac

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Posted 24 October 2011 - 21:26

Thanks for the kind feedback.

Damian, the MJO is pulse of tropical convection that travels eastwards across the tropics. The position and amount of increased convection is charted in phases and it has been suggested that wavelength patterns across the hemispheres are correlated to each phase depending upon the time of year.

Regarding the state of the stratosphere, I have yet to see anything other than positive AO conditions when the stratosphere is cold and the vortex strong. Sadly the correlation is not as convincing the other way around!
Last November stratospheric conditions where such that the cold start of the winter, but not necessarily the extent of cold were suggested, and the more benign conditions that followed were most definitely indicated as the stratosphere cooled dramatically.

Edited by chionomaniac, 24 October 2011 - 21:27 .

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.


#18 lorenzo

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Posted 24 October 2011 - 21:30

This was as far as I got into things last year before distracted.

Some interesting reading here also feel free to translate into user friendly English Chiono !

http://journals.amet...IT%3e2.0.CO%3B2

Netweather Extra       Regional Discussion     Severe Weather     Stratosphere 2013/14        Technical Research         Winter 2013/14

 

My own weather Blog     http://scotlandwx.co.uk/   Updated with a ton of useful links

 

 


#19 Tobor

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Posted 25 October 2011 - 01:58

This is the start of an exciting time ahead..we hope! i enjoy the build up.
Something im still trying to work out is the solar influences on the stratophere and then the troposphere this then influencing the jet stream, and i can only expect this to effect the high pressures cells. anyway that could be looked into later as i wait for a southerly track. il be reading this thread with interest!
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#20 knocker

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Posted 25 October 2011 - 09:52

This is the start of an exciting time ahead..we hope! i enjoy the build up.
Something im still trying to work out is the solar influences on the stratophere and then the troposphere this then influencing the jet stream, and i can only expect this to effect the high pressures cells. anyway that could be looked into later as i wait for a southerly track. il be reading this thread with interest!


Well there is nothing simple about this subject as I'm finding out and that applies to Solar Activity Forcing as well. This is an extract from Stratosphere troposphere Interactions by K. Mohanakumar which may help.

9.15 Solar Activity Forcing on Stratosphere Troposphere Coupling

The stratosphere is postulated to be the seat of many phenomena that are directly related to the rest of the atmosphere. There appears to be a link between the upper part of the atmosphere that is more sensitive to solar changes and the dense lower atmosphere, where the weather phenomenon occur. Since the Sun is the primary source of energy for driving the global energy circulation, one may safely deduce that the solar activity affects the tropospheric weather systems only after the variation in the intensity of the solar radiation has been modified during the passage through the atmosphere. The stratosphere thus holds the key to an understanding of the Sun-weather relationship.
Solar ultraviolet (UV) irradiance variations in ll-year cycles have a direct impact on the radiation and ozone budget of the middle atmosphere. During years with maximum solar activity, the solar UV irradiance is enhanced, which leads to additional ozone production and heating in the stratosphere and above. By modifying the meridional temperature gradient, the heating can alter the propagation of planetary-and smaller-scale waves that drive the global circulation. Although the direct radiative forcing of the solar cycle in the upper stratosphere is relatively weak, it could lead to a large indirect dynamical response in the lower atmosphere through a modulation of the polar night jet and the Brewer-Dobson circulation (Kodera and Kuroda 2002). Such dynamical changes can feedback on the chemical budget of the atmosphere because of the temperature dependence of both the chemical reaction rates and the transport of chemical species.
The total energy output of the Sun's energy varies by only ~1% over a II-year solar cycle. But the extreme UV and X-ray part of the solar spectrum shows more than 2% variations in a solar cycle. Since UV radiation is absorbed by ozone in the stratosphere, the concentration of ozone varies with the intensity of UV radiation (Haigh 1994). This radiative-photochemical mechanism effectively amplifies the solar cycle through a positive feedback with the ozone concentration. Ozone variations thus have a radiative impact on the stratosphere and troposphere, and observations and modeling studies (Matthes et al. 2003) are broadly consistent with the expected radiative forcing.
Observations (Dunkerton 2001; Kodera and Kuroda 2002) and modeling (Gray 2003) studies show that circulation anomalies in the upper and middle stratosphere move poleward and downward during the winter season and are linked to anomalies in wave-induced momentum transport. The anomalous wave forcing by interacting with the mean flow can be regarded as a dynamical mechanism to maintain or even to enhance the amplitude of anomalies as they migrate downward into regions of higher density. Due to the solar cycle, perturbations originating in the tropical upper stratosphere may be transmitted to higher latitudes and lower altitudes by the dynamical mechanism.
It has already been seen that ozone changes have a direct radiative impact on the stratosphere and troposphere. Tropospheric Hadley cell is maintained by processes internal to the troposphere by way of moist deep convection and fluxes of momentum and heat due to synoptic-scale baroclinic waves, and other factors, such as tropical ozone. Owing to the size of the ozone heating anomaly, it is plausible that changes in tropical ozone have a significant effect on the tropospheric jet streams. This direct influence is transmitted to midlatitudes by anomalous fluxes associated with synoptic scales (Haigh et al. 2005). On astronomical timescales, much larger direct solar influence is possible to alter the weather systems in the equatorial region.


Edited by weather ship, 25 October 2011 - 09:53 .

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