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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.

post-4523-0-85359500-1319460356_thumb.jp

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.noaa.gov/products/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

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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.

post-4523-0-55888000-1319467799_thumb.gi

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.

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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.

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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!!

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Hey an excelent post i must say i've learned quite alot. Thanks.

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

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.

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

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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.

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

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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.

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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.

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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.

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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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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.

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One thing to note today is the positive zonal mean winds indicated on the following chart.

post-4523-0-08507900-1319614794_thumb.gi

These wind anomalies are found around 100-200 hPa height and 40-50 Degrees north. This is the jet stream when averaged out across the northern hemisphere. Now look at the mean zonal wind chart forecast and watch the jet stream trend north. The further south we see this the better.

http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/eczm.php?alert=1&forecast=all&var=u&lng=eng

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(Replying to chiono's post #21)

Is this good or bad in terms of prospects for winter, chio?

Thanks

A more northward jet would indicate more unsettled weather for the UK with low pressure crossing (trying) the country.

It shows a continuation of the current pattern we are seeing, becomming more unsettled as we move into November.

Chino.......is this correct?? :)

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The jet being further north would indicate more positive AO conditions to me. So a tighter more zonal weather pattern and less meridional flow throughout the whole of the NH. If you look at the first diagram in the first post, the colder stratosphere positive AO conditions would be indicative.

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One thing to note today is the positive zonal mean winds indicated on the following chart.

These wind anomalies are found around 100-200 hPa height and 40-50 Degrees north. This is the jet stream when averaged out across the northern hemisphere. Now look at the mean zonal wind chart forecast and watch the jet stream trend north. The further south we see this the better.

http://wekuw.met.fu-...l&var=u&lng=eng

Thanks Mr C - any idea how reliable the forecasts are - are they based on ensemble forecasts from things like GFS/ECM?

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    • By iapennell
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      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 and the layer that is directly responsible for the weather that we receive at the surface. 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 below 1hPa at the upper levels. The middle stratosphere is often considered to be around the 10-30hPa level.

      Every winter the stratosphere cools down dramatically as less solar UV radiation is absorbed by the ozone content in the stratosphere. The increasing 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 polar stratosphere in relation to that at mid latitudes, the stronger this vortex becomes. The stratospheric vortex has a strong relationship with the tropospheric vortex below. A strong stratospheric vortex will lead to a strong tropospheric vortex. This relationship is interdependent; conditions in the stratosphere will influence the troposphere whilst tropospheric atmospheric and wave conditions will influence the stratospheric state.
      At the surface 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 and wet southwesterly winds. A weaker polar vortex can contribute to a negative AO with the resultant mild wet weather tracking further south and a more blocked pattern the result. A negative AO will lead to a greater chance of colder air spreading to latitudes further south such as the UK.
       AO chart

      The stratosphere is a far more stable environment then the troposphere below it.
      However, the state of the stratosphere can be influenced by numerous factors – the current solar state, the Quasi Biennial Oscillation (QBO), the ozone content and distribution and transport mechanism, the snow cover and extent indices and the ENSO state to name the most significant. These factors can influence whether large tropospheric waves that can be deflected into the stratosphere can disrupt the stratospheric polar vortex to such an extent that it feeds back into the troposphere.
      Ozone Content in the stratosphere
       Ozone is important because it absorbs UV radiation in a process that warms 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 BDC). The strength of this circulation varies from year to year and can in turn be dictated by other influences. The ozone content in the polar stratosphere has been shown to be destroyed by CFC's permeating to the stratosphere from the troposphere. The overall ozone content in the polar stratosphere will help determine the underlying polar stratospheric temperature, with higher contents of ozone leading to a warmer polar stratosphere. The ozone levels can be monitored here: 
      http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/index.shtml
      One of the main influences on the stratospheric state 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 thought 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 can be critical throughout the winter.
      Diagram of the descending phases of the QBO: (with thanks from http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/index.html )

      The QBO has been shown to influence the strength of the BDC, depending upon what phase it is in. The tropical upward momentum of ozone is stronger in the eQBO , whereas in the wQBO ozone transport is stronger into the lower mid latitudes, so less ozone will enter the upper tropical stratosphere to be transported to the polar stratosphere as can be seen in the following diagram.

      http://www.atmos-chem-phys.net/13/4563/2013/acp-13-4563-2013.pdf
      However, the direction of the QBO when combined with the level of solar flux has also been shown to influence the BDC. When the QBO is in a west phase during solar maximum there are more warming events in the stratosphere, as there is also during an easterly phase QBO during solar minimum, so the strength of the BDC is also affected by this – also known as the Holton Tan effect .
      http://strat-www.met.fu-berlin.de/labitzke/moreqbo/MZ-Labitzke-et-al-2006.pdf
      http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50424/abstract  
      http://onlinelibrary.wiley.com/doi/10.1002/2013JD021352/abstract
      The QBO is measured at 30 hPa and has entered a westerly phase for this winter. As mentioned warming events are more likely during solar maximum when in this westerly phase – with the solar flux below 110 units. Currently, we have just experienced a weak solar maximum and the solar flux heading into winter is still around this mark. This doesn’t rule out warming events, but they will not be as likely – perhaps if the solar flux surges then the chance will increase.
      Latest solar flux F10.7cm:

      http://www.swpc.noaa.gov/products/solar-cycle-progression
      Sudden Stratospheric Warmings:
      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 is a rather dramatic event. Normally the polar night jet at the boundary of the polar vortex demarcates the boundary between warmer mid latitude and colder polar stratospheric air (and ozone levels) and this is very difficult to penetrate. SSWs can be caused by large-scale planetary tropospheric (Rossby) 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 which can seriously disrupt the stratospheric vortex, leading to a slowing or even reversal of the vortex.
      Any SSW will be triggered by the preceding tropospheric pattern - in fact the preceding troposheric pattern is important in disturbing the stratospheric vortex even without creating a SSW.  Consider a tropospheric pattern where the flow is very zonal - rather like the positive AO phase in the diagram above. There has to be a mechanism to achieve a more negative AO or meridional pattern from this scenario and there is but it is not straightforward.  It just doesn't occur without some type of driving mechanism. Yes, we need to look at the stratosphere - but if the stratosphere is already cold and a strong polar vortex established, then we need to look back into the troposphere. In some years the stratosphere will be more receptive to tropospheric interactions than others but we will still need a kickstart from the troposphere to feedback into the stratosphere. This kickstart will often come from the tropics in the form of pulses and patterns of convection. These can help determine the position and amplitude of the long wave undulations Rossby waves - that are formed at the barrier between the tropospheric polar and Ferrel cells. The exact positioning of the Rossby waves will be influenced by (amongst other things) the pulses of tropical convection, such as the phase of the Madden Jullian Oscillation and the background ENSO state and that is why we monitor that so closely. These waves will interact with land masses and mountain ranges which can absorb or deflect the Rossby waves disrupting the wave pattern further - and this interaction and feedback between the tropical and polar systems is the basis of how the Global Wind Oscillation influences the global patterns.
      If the deflection of the Rossby Wave then a wave breaking event occurs – similar to a wave breaking on a beach – except this time the break is of atmospheric air masses. Rossby wave breaks that are directed poleward can have a greater influence on the stratosphere. The Rossby wave breaks in the troposphere can be demonstrated by this diagram below –
      RWB diagram:

      https://www.jstage.jst.go.jp/article/jmsj/86/5/86_5_613/_pdf
       This occurs a number of times during a typical winter and is more pronounced in the Northern Hemisphere due to the greater land mass area. Most wave deflections into the stratosphere do change the stratospheric vortex flow pattern - this will be greater if the stratosphere is more receptive to these wave breaks (and if they are substantial enough, then a SSW can occur). The change in the stratospheric flow pattern can then start to feedback into the troposphere - changing the zonal flow pattern into something with more undulations and perhaps ultimately to a very meridional flow pattern especially if a SSW occurs - but not always. If the wave breaking occurs in one place then we see a wave 1 type displacement of the stratospheric vortex, and if the wave breaking occurs in two places at once then we will see a wave 2 type disturbance of the vortex which could ultimately squeeze the vortex on half and split it – and if these are strong enough then we would see a displacement SSW and split SSW respectively. The SSW is defined by a reversal of mean zonal mean winds from westerly to easterly at 60ºN and 10hPa. This definition is under review as there have been suggestions that other warmings of the stratosphere that cause severe disruption to the vortex could and should be included. http://birner.atmos.colostate.edu/papers/Butleretal_BAMS2014_submit.pdf
      A demonstration of the late January 2009 SSW that was witnessed in the first strat thread has been brilliantly formulated by Andrej (recretos) and can be seen below:
       
      The effects of a SSW can be transmitted into the troposphere as the downward 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. A recent paper has shown how the modelling of SSW and strong vortex conditions have been modelled over a 4 week period. This has shown that there is an increase in accuracy following weak or strong vortex events – though the one area that the ECM overestimates blocking events following an SSW at week 4 is over Northwestern Eurasia.
      http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104007
      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.
      We have also seen in recent years following Cohen's work the importance of the rate of Eurasian snow gain and coverage during October at latitudes below 60ºN. If this is above average then there is enhanced feedback from the troposphere into the stratosphere through the Rossby wave breaking pattern described above and diagrammatically below.
      Six stage Cohen Process:

      The effect of warming of the Arctic ocean leading to colder continents with anomalous wave activity penetrating the stratosphere has also been postulated
      http://www.tos.org/oceanography/archive/26-4_cohen.pdf
      As ever, I will supply links to various stratospheric websites were forecasts and data can be retrieved and hope for another fascinating year of monitoring the stratosphere.
      GFS: http://www.cpc.ncep.noaa.gov/products/stratosphere/strat_a_f/
      ECM/Berlin Site: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html  
      Netweather: https://www.netweather.tv/charts-and-data/stratosphere
      Instant weather maps: http://www.instantweathermaps.com/GFS-php/strat.php
       NASA Merra site: http://acdb-ext.gsfc.nasa.gov/Data_services/met/ann_data.html
      Previous stratosphere monitoring threads:
      2016/17 https://www.netweather.tv/forum/topic/86485-stratosphere-temperature-watch-201617/
      2015/16 https://www.netweather.tv/forum/topic/84231-stratosphere-temperature-watch-20152016/
      2014/2015 https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/
      2013/2014 https://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/
      2012/2013 https://forum.netweather.tv/topic/74587-stratosphere-temperature-watch-20122013/
      2011/2012 https://forum.netweather.tv/topic/71340-stratosphere-temperature-watch-20112012/
      2010/2012 https://forum.netweather.tv/topic/64621-stratosphere-temperature-watch/?hl=%20stratosphere%20%20temperature%20%20watch
      2009/2010 https://forum.netweather.tv/topic/57364-stratosphere-temperature-watch/
      2008/2009 https://forum.netweather.tv/topic/50299-stratosphere-temperature-watch/
    • By iapennell
      As promised I have piece together macroscale developments of sea-surface temperature and regional wind/pressure anomalies to provide a preliminary forecast for the coming winter.During October the global winds, pressure and temperature-patterns across the Northern Hemisphere gravitate towards their winter states, which they will tend to retain until late March.
      First thing though we need to list what we know so far:
      1) Sea surface temperatures are, in general well above normal across the North Atlantic with anomalies close to 4C for early October in the European Arctic section with anomalies of +6C off the eastern coast of the USA and in the Baltic. The section is part of the mid-North Atlantic about 45 to 55N and 20 to 40W where sea surface temperatures are up to 2C colder than usual. Such warmer than usual waters around the UK would directly warm any winds blowing over them more and would tend to support milder weather and more evaporation from the warmer seas would support increased rainfall. The cool patch in the North Atlantic is sufficiently far west for it to cause the southern part of the strong upper Westerlies to re-curve south over it and just to the east whilst the upper air would be encouraged to "re-curve" northwards having crossed the warmer waters around Britain: This would place an upper trough near to the UK and enhance wet, windy weather.  
      2) The North Pacific north of 20N is substantially warmer than normal with sea surface temperature anomalies generally 3 to 4C warmer than normal for early October. However the Equatorial central and eastern Pacific is colder than usual with anomalies up to 2C below normal. The development of La Nina with cool equatorial waters would promote weaker north-easterly Trade Winds over the Pacific between the Equator and a weaker subtropical high-pressure belt centred over warmer than usual waters of the North Pacific around 30 to 35N: Weaker NE Trade Winds impart less westerly atmospheric angular momentum (AAM) to the Northern Hemisphere's atmospheric circulation through frictional interaction with the sea-surface- particularly as less wind means a calmer sea-surface with very low coefficient of friction. There is correspondingly need for less of a sink for accumulated westerly momentum in higher latitudes which implies weaker westerlies reaching Britain with a correspondingly higher chance of cold-air outbreaks from Russia or the Arctic. 
      3) Arctic sea-ice extent has recovered remarkably during September and it's extent is close to the seasonal norm east of Greenland but the sea-ice extent remains some 500 km north of its normal October extent north of Alaska and the extreme east of Siberia. Open waters in the Arctic Ocean surrounding the sea-ice remains substantially (i.e. widely up to 4C warmer than normal for October however): This is likely to encourage the Circumpolar Vortex to be contracted as well as displaced towards the UK by up to 200 km, however the warmth of Arctic seas would encourage the strong baroclinic gradients to be shifted towards the Arctic. This lends support to deeper depressions encircling the Arctic close to 70N, particularly in the North Atlantic sector and the warmth of the oceans just to the south of them means rather more moisture latent-heat potential to fuel these storms. The northwards displacement of the Westerlies is likely to encourage them to be strong in any case because they have to blow harder closer to the axis of the Earth's rotation to offset the tropical, subtropical and polar easterlies as required by Conservation of Angular Momentum laws.
      4) Also supportive of a mild wet and windy winter is the fact that the Quasi Biennial Oscillation (QBO) at 30mb high above the Equator remains in Westerly phase. During August these stratospheric Equatorial Winds averaged just over 10 metres per second (23 mph) from the west. These stratospheric winds feed down into the general circulation and reach the mid-latitude jet-streams and Westerlies over three or four months. This suggests (strongly) that the coming winter will be mild wet and stormy.
      5) The Sun is now entering the quiet phase towards the end of Schwabe cycle 24: Indications are that the Sun is indeed going quieter than it has been for a few years. An active Sun produces Solar Flares which interact with the atmospheric circulation to increase the strength of the Circumpolar Vortex. Instead few (if any) magnetic storms from the Sun will be interacting with the Earth's atmosphere and instead (if anything) that just leaves tidal friction due to the Sun and Moon which affects the atmosphere as well as the oceans. The tidal effects on the atmosphere are very weak but these act to reduce the Earth's rotation by very mall amounts (these are significant over time, which is why Leap Seconds are added at the end of each year). The net effect of all this (weak phase of Solar Cycle, atmospheric tidal friction) would be to weaken the Westerlies a little.
      6) At least until mid November, the fact that sea-surface temperatures in the tropical Atlantic and Pacific just north of the Equator is likely to enhance tropical storm activity. More hurricanes and typhoons with strong easterlies on their northern flanks that enter the Northern Hemisphere circulation add Westerly AAM to the global atmospheric circulation. This increases the need for stronger Westerlies in higher latitudes to counter-balance them: This strongly hints to late autumn/early winter being wet, mild and stormy. However, from late January onwards the Intertropical Convergence Zone (ITCZ) will be south of the Equator and the fact that sea-surface temperatures in tropical waters just south of the Equator are also warmer than normal now suggests more tropical storms will occur there; Southern Hemisphere tropical depressions (sliding westwards along the ITCZ) have strong westerlies on their northern flank and it is these that will affect the Angular Momentum Budget of the Northern Hemisphere circulation by removing Westerly AAM through frictional impact with the underlying surface: This points to weaker Westerlies coming across the North Atlantic in January/February which would, other things being equal, increase the chances of much colder, drier spells reaching Britain from the east.  
      We can now put all this together to get some sort of prediction for Winter 2016/17:
      (Continued below)
    • By chionomaniac
      Welcome to the latest stratospheric temperature watch thread.
       
      A bit later this year with a new thread – but better late than never! It is now the 7th winter stratospheric temperature watch thread on netweather, and how much have we learnt in the past years!
       
      As ever, the first post will become both a reference thread and basic learning thread for those wanting to understand how the stratosphere may affect the winter tropospheric pattern, so forgive me for some repeat from previous years, but it is important that those new to the stratosphere have a place that they can be directed to in order to achieve a basic grasp of the subject.
       
      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 and the layer that is directly responsible for the weather that we receive at the surface. 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 below 1hPa at the upper levels. The middle stratosphere is often considered to be around the 10-30hPa level.
       

       
      Every winter the stratosphere cools down dramatically as less solar UV radiation is absorbed by the ozone content in the stratosphere. The increasing 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 polar stratosphere in relation to that at mid latitudes, the stronger this vortex becomes. The stratospheric vortex has a strong relationship with the tropospheric vortex below. A strong stratospheric vortex will lead to a strong tropospheric vortex. This relationship is interdependent; conditions in the stratosphere will influence the troposphere whilst tropospheric atmospheric and wave conditions will influence the stratospheric state.
       
      At the surface 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 and wet southwesterly winds. A weaker polar vortex can contribute to a negative AO with the resultant mild wet weather tracking further south and a more blocked pattern the result. A negative AO will lead to a greater chance of colder air spreading to latitudes further south such as the UK.
       
       AO chart
       

       
      The stratosphere is a far more stable environment then the troposphere below it.
      However, the state of the stratosphere can be influenced by numerous factors – the current solar state, the Quasi Biennial Oscillation (QBO), the ozone content and distribution and transport mechanism, the snow cover and extent indices and the ENSO state to name the most significant. These factors can influence whether large tropospheric waves that can be deflected into the stratosphere can disrupt the stratospheric polar vortex to such an extent that it feeds back into the troposphere.
       
      Ozone Content in the stratosphere
       
       Ozone is important because it absorbs UV radiation in a process that warms 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 BDC). The strength of this circulation varies from year to year and can in turn be dictated by other influences. The ozone content in the polar stratosphere has been shown to be destroyed by CFC's permeating to the stratosphere from the troposphere. The overall ozone content in the polar stratosphere will help determine the underlying polar stratospheric temperature, with higher contents of ozone leading to a warmer polar stratosphere. The ozone levels can be monitored here: 
       
      http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/index.shtml
       
      One of the main influences on the stratospheric state 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 thought 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 can be critical throughout the winter.
       
      Diagram of the descending phases of the QBO: (with thanks from http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/index.html )
       

       
       
      The QBO has been shown to influence the strength of the BDC, depending upon what phase it is in. The tropical upward momentum of ozone is stronger in the eQBO , whereas in the wQBO ozone transport is stronger into the lower mid latitudes, so less ozone will enter the upper tropical stratosphere to be transported to the polar stratosphere as can be seen in the following diagram.
       

       
      http://www.atmos-chem-phys.net/13/4563/2013/acp-13-4563-2013.pdf
       
      However, the direction of the QBO when combined with the level of solar flux has also been shown to influence the BDC. When the QBO is in a west phase during solar maximum there are more warming events in the stratosphere, as there is also during an easterly phase QBO during solar minimum, so the strength of the BDC is also affected by this – also known as the Holton Tan effect .
       
      http://strat-www.met.fu-berlin.de/labitzke/moreqbo/MZ-Labitzke-et-al-2006.pdf
      http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50424/abstract  
      http://onlinelibrary.wiley.com/doi/10.1002/2013JD021352/abstract
       
       
      The QBO is measured at 30 hPa and has entered a westerly phase for this winter. As mentioned warming events are more likely during solar maximum when in this westerly phase – with the solar flux below 110 units. Currently, we have just experienced a weak solar maximum and the solar flux heading into winter is still around this mark. This doesn’t rule out warming events, but they will not be as likely – perhaps if the solar flux surges then the chance will increase.
       
      Latest solar flux F10.7cm:
       

       
      http://www.swpc.noaa.gov/products/solar-cycle-progression
       
       
      Sudden Stratospheric Warmings:
       
      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 is a rather dramatic event. Normally the polar night jet at the boundary of the polar vortex demarcates the boundary between warmer mid latitude and colder polar stratospheric air (and ozone levels) and this is very difficult to penetrate. SSWs can be caused by large-scale planetary tropospheric (Rossby) 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 which can seriously disrupt the stratospheric vortex, leading to a slowing or even reversal of the vortex.
       
       
      Any SSW will be triggered by the preceding tropospheric pattern - in fact the preceding troposheric pattern is important in disturbing the stratospheric vortex even without creating a SSW.  Consider a tropospheric pattern where the flow is very zonal - rather like the positive AO phase in the diagram above. There has to be a mechanism to achieve a more negative AO or meridional pattern from this scenario and there is but it is not straightforward.  It just doesn't occur without some type of driving mechanism. Yes, we need to look at the stratosphere - but if the stratosphere is already cold and a strong polar vortex established, then we need to look back into the troposphere. In some years the stratosphere will be more receptive to tropospheric interactions than others but we will still need a kickstart from the troposphere to feedback into the stratosphere. This kickstart will often come from the tropics in the form of pulses and patterns of convection. These can help determine the position and amplitude of the long wave undulations – Rossby waves - that are formed at the barrier between the tropospheric polar and Ferrel cells. The exact positioning of the Rossby waves will be influenced by (amongst other things) the pulses of tropical convection – such as the phase of the Madden Jullian Oscillation and the background ENSO state and that is why we monitor that so closely. These waves will interact with land masses and mountain ranges which can absorb or deflect the Rossby waves disrupting the wave pattern further - and this interaction and feedback between the tropical and polar systems is the basis of how the Global Wind Oscillation influences the global patterns.
       
       
      If the deflection of the Rossby Wave then a wave breaking event occurs – similar to a wave breaking on a beach – except this time the break is of atmospheric air masses. Rossby wave breaks that are directed poleward can have a greater influence on the stratosphere. The Rossby wave breaks in the troposphere can be demonstrated by this diagram below –
       
      RWB diagram:
       

       
      https://www.jstage.jst.go.jp/article/jmsj/86/5/86_5_613/_pdf
       
       
       
       This occurs a number of times during a typical winter and is more pronounced in the Northern Hemisphere due to the greater land mass area. Most wave deflections into the stratosphere do change the stratospheric vortex flow pattern - this will be greater if the stratosphere is more receptive to these wave breaks (and if they are substantial enough, then a SSW can occur). The change in the stratospheric flow pattern can then start to feedback into the troposphere - changing the zonal flow pattern into something with more undulations and perhaps ultimately to a very meridional flow pattern especially if a SSW occurs - but not always. If the wave breaking occurs in one place then we see a wave 1 type displacement of the stratospheric vortex, and if the wave breaking occurs in two places at once then we will see a wave 2 type disturbance of the vortex which could ultimately squeeze the vortex on half and split it – and if these are strong enough then we would see a displacement SSW and split SSW respectively. The SSW is defined by a reversal of mean zonal mean winds from westerly to easterly at 60ºN and 10hPa. This definition is under review as there have been suggestions that other warmings of the stratosphere that cause severe disruption to the vortex could and should be included. http://birner.atmos.colostate.edu/papers/Butleretal_BAMS2014_submit.pdf
       
      A demonstration of the late January 2009 SSW that was witnessed in the first strat thread has been brilliantly formulated by Andrej (recretos) and can be seen below:
       

       
       
      The effects of a SSW can be transmitted into the troposphere as the downward 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. A recent paper has shown how the modelling of SSW and strong vortex conditions have been modelled over a 4 week period. This has shown that there is an increase in accuracy following weak or strong vortex events – though the one area that the ECM overestimates blocking events following an SSW at week 4 is over Northwestern Eurasia.
       
      http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104007
       
      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.
       
      We have also seen in recent years following Cohen's work the importance of the rate of Eurasian snow gain and coverage during October at latitudes below 60ºN. If this is above average then there is enhanced feedback from the troposphere into the stratosphere through the Rossby wave breaking pattern described above and diagrammatically below.
       
      Six stage Cohen Process:
       

       
       
      The effect of warming of the Arctic ocean leading to colder continents with anomalous wave activity penetrating the stratosphere has also been postulated
       
      http://www.tos.org/oceanography/archive/26-4_cohen.pdf
       
       
      Last year we saw a large snow gain but unfortunately tropospheric atmospheric patterns prevented the full potential of these being unleashed on the stratosphere – hence no SSW, but this winter could be different, but we will have to wait until the end of October.
       
       
       ENSO Influences
       
      One of the main influences in the global atmospheric state this winter will be the upcoming El Nino, and that is forecast to be the strongest since 1997. Studies have shown that SSW’s are more likely during strong ENSO events ( http://www.columbia.edu/~lmp/paps/butler+polvani-GRL-2011.pdf) 
       but also that there is a particular pattern of upward propagating waves. During El Nino events wave formation is suppressed over the Indian Ocean Basin whilst it is enhanced over the Pacific Ocean
       
      http://link.springer.com/article/10.1007%2Fs00382-015-2797-5
       
      The ENSO pathway taken may be all critical this year as can be demonstrated by this paper  http://www.columbia.edu/~lmp/paps/butler+polvani+deser-ERL-2014.pdf
       
      This can lead us to suggest that a rather distinctive wave 1 pattern is likely this winter with the trigger zone likely to be over the north Pacific in the form of a quasi stationary enhanced wave 1 – a traditional Aleutian low SSW trigger pattern is suggested by Garfinkel et al ( http://www.columbia.edu/~lmp/paps/garfinkel+etal-JGR-2012.pdf ) and this should be expected at some point this winter.
       
       
       

       
       
       
      The reported incidence of SSW in EL Nino years is roughly around 60%  - which is more than ENSO neutral years.  A big question remains however, whether the ENSO wave 1 pattern will override the negative HT effect that the wQBO with the reducing solar ouput link brings. And even if it does, and we do achieve a displacement SSW, the next question is how will this affect the Atlantic sector of the Northern Hemisphere? My suspicion is that even if we do achieve a SSW this winter it will be in the second half, and also any subsequent blocking may not be quite right for the UK and, that if we were to achieve a –ve NAO, any block will be nearer Canada than Iceland, leaving the Atlantic door ajar.  It is still too early this winter to be making any definitive forecasts – the next 6 weeks are very important stratospherically, determining in what vein winter will start. Already we are seeing a forecast of weak wave activity disrupting the growing vortex and it will be interesting to see if this is repeated during November.
       
      And it will be especially interesting to see what occurs in November and what is forecast for December before winter starts because typical strong El nino wQBO stratospheric composite analogues tell an opposite story. They suggest that the stratospheric vortex will be disrupted and weaker early in the winter before gaining in strength by February.
       
      December:
       

       
      January
       

       
      February
       

       
      The mean zonal winds are already forecast to be below average so perhaps an early disrupted vortex is more likely this year!
       

       
      As ever, I will supply links to various stratospheric websites were forecasts and data can be retrieved and hope for another fascinating year of monitoring the stratosphere.
       
       
       
      GFS: http://www.cpc.ncep.noaa.gov/products/stratosphere/strat_a_f/
       
      ECM/Berlin Site: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html  
       
      Netweather: http://www.netweather.tv/index.cgi?action=stratosphere;sess=75784a98eafe97c5977e66aa65ae7d28
       
      Instant weather maps: http://www.instantweathermaps.com/GFS-php/strat.php
       
       NASA Merra site: http://acdb-ext.gsfc.nasa.gov/Data_services/met/ann_data.html
       
       
      Previous stratosphere monitoring threads:
       
      2014/2015 https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/
       
      2013/2014 https://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/
       
      2012/2013 https://forum.netweather.tv/topic/74587-stratosphere-temperature-watch-20122013/
       
      2011/2012 https://forum.netweather.tv/topic/71340-stratosphere-temperature-watch-20112012/
       
      2010/2012 https://forum.netweather.tv/topic/64621-stratosphere-temperature-watch/?hl=%20stratosphere%20%20temperature%20%20watch
       
      2009/2010 https://forum.netweather.tv/topic/57364-stratosphere-temperature-watch/
       
      2008/2009 https://forum.netweather.tv/topic/50299-stratosphere-temperature-watch/
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