chionomaniac

Of course a nino based AAM atmosphere will encourage this and the amount of Ozone ready to be transported from the tropics. The tropical stratosphere at 10hPa is currently running at 5ºC below average and this has reduced the thermal differerential by about a third between that and the polar stratosphere. it will be interesting to see how this is affecting the mean zonal mean winds at 60ºN (when I can find a site that is accurately measuring this presently)

From what I have read from the dodgy google translate the research looks really interesting and I can't wait for the English paper translation.

It is too early in the season to get a SSW - the vortex is just about to get going. My guess is that the stratospheric cooling taking place will gather momentum - with perhaps a slight delay. Encouraging though to see a NH strong MT this early in the autumn.Will look at it in a bit more detail later.

I often find it difficult to describe the coupling of the stratosphere with the troposphere, however I am going to try an analogy. For those who watch Come Dancing, then perhaps this will be easier to understand. The stratosphere/troposphere couple during winter are like a pair of dancers. However, this is no couple where one dancer takes the dominant lead - rather, we see a swapping of leads between the troposphere and the stratosphere during the dance. Occasionally, one will leave the other ( for instance a non propagating SSW) only to join up later. Generally, where one places their foot the other moves their own accordingly, so that the flow of the dance is kept and a symmetry is maintained. On other occasions one dancer (the stratosphere) can become the lead dancer and firmly clasps the other dancer (when it becomes very cold and increased in strength - vortex intensification) and that dancer (the troposphere) can not let go until the other dancer relaxes their grip (giving stratospheric led positive AO conditions). That grip can be relaxed instantly though by the other dancer tripping the lead dancer up ( through a SSW that will be tropospherically led by MT wave breaking) and the speed of the dance reduces or stops dramatically. The fact though, is that during winter those two dancers are dynamically linked and anyone who looks at one without looking at the other will be judging the dance falsely or blindly - it would be akin to judging Torvill and not Dean or Dean and not Torvill, when in fact they were both dancing together all of the time!

My answer would always be yes. Firstly, a blocked pattern is more likely to lead to a SSW - it's all part of the troposphreric/ stratospheric feedback mechanism and any SSW is likely to prolong a blocked pattern, not shorten it imo. Just as MS has said above!!

Thanks for those links Matt - will bookmark. And welcome to Netweather Geoff.

For those who spend a lot of time looking at the CFSv2 monthly forecast charts it is worth reading the following abstract. Effectively, I read that as suggesting that the predicted AO winter values are underestimating the contribution of the stratospheric feedback from October Eurasion snow gain. If anyone has a spare £30 then they can get the whole paper! Abstract Lagged ensembles from the operational Climate Forecast System version 2 (CFSv2) seasonal hindcast dataset are used to assess skill in forecasting interannual variability of the December–February Arctic Oscillation (AO). We find that a small but statistically significant portion of the interannual variance (>20 %) of the wintertime AO can be predicted at leads up to 2 months using lagged ensemble averages. As far as we are aware, this is the first study to demonstrate that an operational model has discernible skill in predicting AO variability on seasonal timescales. We find that the CFS forecast skill is slightly higher when a weighted ensemble is used that rewards forecast runs with the most accurate representations of October Eurasian snow cover extent (SCE), hinting that a stratospheric pathway linking October Eurasian SCE with the AO may be responsible for the model skill. However, further analysis reveals that the CFS is unable to capture many important aspects of this stratospheric mechanism. Model deficiencies identified include: (1) the CFS significantly underestimates the observed variance in October Eurasian SCE, (2) the CFS fails to translate surface pressure anomalies associated with SCE anomalies into vertically propagating waves, and (3) stratospheric AO patterns in the CFS fail to propagate downward through the tropopause to the surface. Thus, alternate boundary forcings are likely contributing to model skill. Improving model deficiencies identified in this study may lead to even more skillful predictions of wintertime AO variability in future versions of the CFS. http://link.springer.com/article/10.1007%2Fs00382-013-1850-5 Also one of the SSW's that interest me this winter is the one from 2009. If we recap then this occurred early Feb 2009 in a west QBO during solar MINIMUM - previously unheard of. This occurred during the first strat temp watch thread and I remember our surprise at this event at the time. There is another comparitive study that showed that the pre-SSW period in 2009 was characterized by a peak in the 100 hPa eddy heat flux with a predominance of wave number 2 activity. This was due to strong anomalies associated with Rossby wave packets originating from a deep ridge over the eastern Pacific. http://onlinelibrary.wiley.com/doi/10.1029/2010JD015023/abstract So that is what we will need to look out for and monitor this winter - the 100hPa heat flux - especially in January. As soon as the US govt sites are back then I will go straight to the composites to look at analogue years for that and East Pacific Ridges in January. In fact I have aleady looked up H500 anomaly for January analogue years and guess what? Yes - big signal for that East Pacific ridge. More credence to that split SSW early Feb theory?

Labitzke, who has completed this study, states that solar max is above 150 units (10.7cm) of flux during Jan/Feb. So going by that we are heading well below that value for this winter - though there has been a SSW in wQBO and similar solar conditions. http://strat-www.met.fu-berlin.de/labitzke/moreqbo/MZ-Labitzke-et-al-2006.pdf

Yes and no. I was in particular referring to the the last phase which was from 1999-2012 against the climatological mean of 1981 -2010. I would expect over the whole NH to have areas of positive anomalies and negative anomalies similar to 1950-1975, even allowing for the change in base state. With the composite building site still out of bounds I can't have a play around to demonstrate this. If the climatology comparison was using the years 1950-2010 I don't think the composites would look too different - though I could be wrong without checking.

Interesting that the last cycle shows no negative anomaly areas though Recretos - so one would think that there is more at play here - hence the difference being the low sea ice link? Oh and to edit - love the phrase the 'gatekeepers'.

I see the first signs in FI that a more traditional autumnal pattern is likely to become more dominant. I suspect that we will see the modelling come into line with a more October MJO phase 2 type pattern as we get closer to November. That will involve a reduction in heights in Greenland with a more mobile Atlantic pattern and probable height build up to our NE. How far north the jet stream settles across the Atlantic remains to be seen. Wet and mild will be the theme by the end of the month is my best guess with recurrent troughing towards the west of the country.

Agree with that - Stewart will be missed greatly. I think that by the end of November we will see where that prediction is heading. I think that if the strat cools down less quickly than anticipated then we may even be able to bring the feedback schedule through a bit quicker. The low sea ice years 500 hpa anomaly give us a massive tropospheric headstart.

Yep. New thread here: http://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/

With winter fast approaching it is time for a new thread. It seems that the demand for a new strat thread gets earlier every year and this is the fifth winter that the strat thread will be running! 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. And then I will have a look at how we may expect the stratosphere to behave this year. 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 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 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 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. So cold lovers will look out for a warmer than average polar stratosphere. 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.fu-berlin.de/labitzke/moreqbo/MZ-Labitzke-et-al-2006.pdf) (http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50424/abstract) The QBO is measured at 30 hPa and has entered a westerly phase for this winter. 10 out of 11 warming events that have occurred during a wQBO have occurred at a solar maximum. Even though we are seeing a quiet maximum one would expect a slightly increased chance of a warming event this winter. 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 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 (such as the eQBO) but we will still need a kick start from the troposphere to feedback into the stratosphere. The kick start often will come from the tropics in the form of pulses of convection interacting with slight undulations in the polar vortex which influence the positions of the sub tropical jet stream and polar jet streams respectively. The exact positioning of the large scale undulations ( or Rossby waves) will be influenced by (amongst other things) the pulses of tropical convection ( aka the phase of the MJO) 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. The ENSO state can affect this - giving us the underling atmospheric base state . If the deflection of the Rossby Wave is great enough then the wave can be deflected into the stratosphere. This occurs a number of times during a typical winter and is more pronounced in the NH 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. 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. We have also seen in recent years following Cohen's work the importance of the rate of Eurasian snow gain 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 it appears that the reduction in Arctic sea ice may be contributing to this mechanism and this should be factored in to any forecast. So what are we likely to expect this year. Well, so far we know some of the factors. There is a wQBO combined with probable ENSO neutral conditions and even though we are at a possible solar maximum, this is about half the maximum seen in recent times. However, I think that there is still a strong possibility that we will see a SSW - possibly late January or early February this winter. Using similar years analogues we can help predict the likely stratospheric conditions for this year. Unfortunately, there is a shortage of comparable years that meet the above data - but at least we can get an idea. And with another low Arctic sea ice year and early snow gain already then perhaps by the end of the month confidence can increase. Here is the predicted stratospheric height anomaly pattern for this winter at 30 hPa. November Here we see a strong central vortex beginning to build that is well established by Dec December However the height anomaly at latitudes south of the vortex suggest to me that there is some wave propagation from the troposphere - and this builds through January January before overwhelming the vortex and weakening it during February ( remember that the anomaly's are for the whole month and the vortex will have recovered somewhat from any warming episode) February - Split type SSW? The suggested pattern of warming at 30 hPa for January and February are as follows: January Feb So, during the coming months we will need to keep an eye on all the stratospheric data. Here are the links: Forecasts: ECM http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html GFS http://www.cpc.ncep.noaa.gov/products/stratosphere/strat_a_f/ and here: http://www.netweather.tv/index.cgi?action=stratosphere;sess=75784a98eafe97c5977e66aa65ae7d28 http://www.instantweathermaps.com/GFS-php/strat.php Analysis here: http://acdb-ext.gsfc.nasa.gov/Data_services/met/ann_data.html and here: http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/ Many papers for further reading found here: http://forum.netweather.tv/topic/73911-technical-teleconnective-papers/ Fingers crossed for another exciting and productive stratospheric watch this winter. c

That chart is fine for here. To clarify, wintry (and any other type of weather) potential for this winter is fine in this thread, however, wintry potential for Autumn should be in the autumn thread.

Interesting pattern coming up. Interestingly it highlights the theory that all that glitters is not necessarily gold. Here we see the ensemble anomaly plot with fantastic heights over Greenland - but in this case the transfer of the trough across the Atlantic doesn't happen and therefore does not allow heights to rebuild behind and link with Greenland. This prevents the release of the cold from further north. It shows that heights over Greenland does not guarantee cold here. All said, I think I would rather see this west based -ve NAO pattern now, than in the middle of winter!

Yes, I agree with this Please keep this thread for upcoming winter discussion only. Any off topic posts will be deleted or removed. If you would like to discuss the GFS/ECM autumnal wintry potential then please post in the Autumn thread. Thanks.

Still no vortex build up over Greenland and a far more southerly positioned jet stream over the Atlantic. Even if the trough reaches the UK then I suspect there could be a rebuild of heights behind following in line with the NAEFS chart I showed moments ago.

Please back this statement up Ian with evidence supplied from the output. I can provide evidence to the contrary within seconds, such as this NAEFS ensemble spread which shows positive anomalies over Greenland which will disrupt a strong vortex settling there. If you can't then I will assume that your postings are a deliberate attempt to troll and will be removed as if they are such.

I suspect that was a link to the previous run - because that is certainly not a Bartlett.

No, It's a good thing all things considered. Anything that can interupt a straightforward cooling of the autumnal strat could be beneficial. Worth keeping an eye on - Late November cold anyone? Edit - just as aside to this is that anyone who monitors the strat regularly will know that there is often some sort of degree of warming in FI runs and that we will need to link them up to possible MT / wave breaking events this winter to determine which ones are more likely to come to fruition.

Conor, if you managed to track down that chart and manage to post it then you are halfway there to finding the info to answer your own question. As a learning exercise have a go at answering your own question. Do you think it would be cold and if so, why and what do you think the surface conditions would be?

If we can have a rinse and repeat of tonights ECM in exactly 3 months time (with verification guaranteed) then I think a lot would be very happy on here. Certainly looks like a perfect retrogression on this run.

Was looking up record strat NAM months and I am coming acrioss papers so I will dump them in here and read later The first looks really interesting reagrding cold spells over N Europe http://www.nwra.com/resumes/baldwin/pubs/TomassiniEtAl2012.pdf http://www.phys.ocean.dal.ca/people/po/Whistler/baldwin.pdf We may already have this one linking the MJO: http://www.jhu.edu/~dwaugh1/papers/Garfinkel_etal_2012_mjo.pdf http://www.atmos.pku.edu.cn/yhu/2010-2011-winter.pdf

Thanks. I have sen them floating about for a while now but didn't know where the site was.