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chionomaniac

Stratosphere Temperature Watch

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From chionomaniac

I reckon that link is just for over the North Pole whereas the NOAA one is the mean average anomaly from 60N to 90N. So it may be slightly warmer over the North Pole but cooler in the latitudes north of 60N.

In that case, could the brief warming event at the beginning of November be reflected in the height rises over tepole now?

It is thought that any significant stratospheric warming event will take around 6 weeks to filter down to the troposphere to cause any effect on our weather. So we will not really know how the slight warming at the start of this month affects us, if at all, for some time yet.

When you look at an overlay view of the polar stratospheric temperature it is possible to imagine the vortex circling the northern hemisphere, and how, even though a pool of colder air is expanding between 60N and 90N, that the temperature right over the pole may be slightly less cold but overall this may not be as significant as the graph Azores Hi provides a link to.

Look below - is the North Pole colder on the 13Nov or the 17 Nov?:

The answer is that the North Pole is probably slightly warmer on the 17th but overall the cold pool between 60N and 90N is greater on the 17th as well. So the average temp of the stratosphere is colder on the 17th and is still cooling as expected at this time of year. I would only sit up and get excited when the 30hPa temp at the North Pole rises significantly and in conjunction with an event affecting the whole vortex.

c

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so i assume that this northwesterly flow could continue for some time, with things only slightly above average in stratospheric temperature. at the moment though, no prolonged northerly blocking looking likely for the uk, just the odd 2 day cold snap occurring now and then, however, we should keep an eye out for around mid december? in the hope that short warming event could produce a slightly longer northerly than we are used to.

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so i assume that this northwesterly flow could continue for some time, with things only slightly above average in stratospheric temperature. at the moment though, no prolonged northerly blocking looking likely for the uk, just the odd 2 day cold snap occurring now and then, however, we should keep an eye out for around mid december? in the hope that short warming event could produce a slightly longer northerly than we are used to.

What is happening up in the stratosphere now and what is occurring in the troposphere now (ie this weekend's northerly) are two entirely different things and I feel it is important to stress that slight temperature changes in the stratosphere this month will not affect the potency/duration of the current weather.

I will be keeping an eye out in mid December only as an interested observer, not because I expect the small rise in stratospheric temp directly over the North Pole at the start of the month will have some dramatic influence. In fact, if one looks at the temp mean anomaly chart (for 60N-90N) for the start of the month you will see that the temp fluctuates between 4ºC above and 4ºC below average. No significant warming event there then!

c

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With no imminent sign of surface cold being displaced from the arctic, and factoring in other teleconnnections, I predict December to be mild and stormy.

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With no imminent sign of surface cold being displaced from the arctic, and factoring in other teleconnnections, I predict December to be mild and stormy.

care to elaborate

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Latest update:

Both the ECM and NOAA have similar predictions for 5 days out:

.

Regards

c

Just like to say that these predictions were pretty close for 20th Nov:

So just for fun I will have a look out to T+240. More interesting this one, with some warming forecast west of Alaska - something to keep an eye on - but with a JH health warning attached!

c

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care to elaborate

Hi Barry, apologies for the delay as I haven't visited this thread for a couple of days. To elaborate it seems clear to me that the 'Polar' stratosphere (60deg north and above) is cool and actually cooling down further...

time_pres_TEMP_ANOM_OND_NH_2008.gif

As I interperet it, this together with the particularly strong thermal gradient over the Pacific could help amplify the jet stream and displace the mid atlantic high to the south allowing for a more zonal flow, temporarily at least. The charts chionomaniac have posted up clearly show the cool polar stratospheric field with the warm anomaly currently south of 60n. As the time lag for the effects to take place at the surface is about a month, I believe the current colder projections in the models will not last much beyond the first week of December, thereafter I believe the transition to milder/zonal synoptics will evolve.

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i think there are signs of the cold air getting displaced, and i think we are heading towards a chilly december.

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The thing is tohugh note where the cold anomalies are setting up. Last 2 years it has been right over Greenland region which allowed a strong PV to form there.

This time round its a good bit east of there to the NE of sCandinavia, thats a big difference from the last few years and means that we do have a shot at getting more colder set-ups simply because you can get some meaningful upper highs in the Mid-Atlantic ridging up, unlike previous winters where a big poler vortex just sat there preventing that from occuring.

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The thing is tohugh note where the cold anomalies are setting up. Last 2 years it has been right over Greenland region which allowed a strong PV to form there.

This time round its a good bit east of there to the NE of sCandinavia, thats a big difference from the last few years and means that we do have a shot at getting more colder set-ups simply because you can get some meaningful upper highs in the Mid-Atlantic ridging up, unlike previous winters where a big poler vortex just sat there preventing that from occuring.

Longer term the NOAA forecast seems to want to return the vortex over Greenland whereas the ECM would like to keep it where it is. Time will tell!

I have been reading further into Stratospheric Sudden Warmings (SSWs) and feel I should put down some main points.

For identification of SSWs (WMO definition) is as follows: A major midwinter warming occurs when the zonal mean zonal winds at 60ºN and 10 hPa become Easterly during winter. So a slight weakening and temperature is not enough to become a SSW. The first day of the reversal of these winds is considered the start of the SSW. The best chart to check for this is http://www.cpc.ncep.noaa.gov/products/stra...OND_NH_2008.gif

The chances of having a SSW in any winter is about 62%.

There are 2 types of SSW - a vortex displacement warming and a vortex split warming. As the names suggest a vortex displacement SSW involves the vortex to be nudged to one side from the Pole, often into a comma shape, by geopotential height rises whereas the vortex split leaves two separate vortices away from the pole. The lead up to and future troposphere response is slightly different for both events. Firstly, a split vortex SSW is more likely to occur in January or February, when the vortex is strongest. A vortex displacement SSW has an even distribution throughout November to March. The wind deceleration that accompanies each SSW, prior to the start date, is far greater with a vortex split than with a displacement. It has been suggested that some kind of preconditioning extends into the troposphere with vortex splits with it being weak and small.

The tropospheric impact at a level of 1000 hPa has been examined between 0 and 60 days after the start date of a SSW. A familiar pattern is found for displacement vortx SSWs: an increase in geopotential height over the polar cap and a reduction in geopotential height in the midlatitude North Atlantic ( a negative NAO). In contrast the geopotential height anomalies following the vortex splits have a much more global character and over Eurasia and significantly over the Pacific Ocean (reminiscent of a positive PNA). In fact these positive Pacific geopotential heights have been noted up to 60 days before a vortex split - something that we can keep an eye on.

I have just scraped the surface here but hopefully increased some understanding a little.

Most info with thanks from this article:

A new look at Stratospheric Sudden Warming events: Part I. Climatology and Modelling Benchmarks, A.J. Charlton and L.M. Polvani, Journal of Climate, 20, 449-469 (2007)

c

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thanks for that C

I find my old brain has great difficulty in trying to understand this, to me new, fascinating view of events so far up.

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Latest update:

Firstly, a bit of depressing news following the airing of the first online video discussion. On that, Brickfielder seemed to suggest that it will be very unlikely to get any warming event in the stratosphere this winter due to the westerly QBO phase that we are now in. Looking back there has been 2 SSWs in the last 25 years when the QBO has been westerly - in Dec 1987 and March 2000, so all hope is not lost, but obviously an easterly QBO would be far more favourable.

http://www.cdc.noaa.gov/Correlation/qbo.data

http://www.appmath.columbia.edu/ssws/index.php

Back to now and the stratosphere appears to be undergoing rapid cooling:

However forecasts suggest that this cooling below average will be reversed:

This is due to a warmer anomaly forecast to be forming west of Alaska:

This was initially forecast on the 10 day forecast 5 days ago as seen in post 57 on the 21st Nov and has grown in size. It has the effect of displacing the vortex slightly towards Siberia. Whether this is enough to cause any further effects down the line remains to be seen.

c

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We are still on track to see the stratosphere warm up in the next few days.

The current temp at the North Pole is below average but I am sure we are about to see it rise: http://ds.data.jma.go.jp/tcc/tcc/products/...e/pole30_n.html.

The zonal wind anomaly is decreasing and will hopefully go negative in the next few days:

http://www.cpc.ncep.noaa.gov/products/stra...OND_NH_2008.gif

The forecast seems to suggest so:

Looking three days ahead there is a nice warm pool at 30hPa developing, which if anything is greater than it was for the 10 day forecast. This is displacing the colder vortex slightly. I have to say if this verifies then the 10 day forecast will be pretty accurate. With the tropospheric polar vortex disrupted presently it will be good to see any cooling of the stratosphere disrupted as well.

Looking further afield, it is worth having a look at the next 10 day forecast which suggests that the warm anomaly diminishes.

I will compare this to see how well it verifies.

c

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With winter starting tomorrow it is worth seeing where we are.

Firstly, we enter winter with the North Pole 30hPa stratospheric temp above average. Well only just!

.

The situation is that the stratospheric polar vortex is centered over the north coast of Siberian Russia. At present it is around average strength for this time of year.

Temperature wise, one can see that there is a warm anomaly centered over the North Pacific west of Alaska. This was forecast 10 days ago and has come pretty close to forecast as can be seen by the charts below. If anything the warm anomaly is slightly greater than forecast.

Now:

Forecast 10 days ago:

The current zonal wind anomalies are trending slightly negative at present:

The future forecast are for the zonal winds to reduce further before increasing again. The temperature which is inversely correlated to the zonal winds is forecast to rise a little bit more before dropping again.

It is a mixed bag looking at the longer term effects for the troposphere. We should be grateful that the westerly phase QBO has not increased the zonal winds more than they are and therefore the stratosphere has not cooled significantly below average as we enter winter. Whether this will continue to be the case only time will tell.

c

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thanks very much for that post C, I'm still learning but its very interesting from my limited understanding of it - still no really clear signal I would think?

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thanks very much for that post C, I'm still learning but its very interesting from my limited understanding of it - still no really clear signal I would think?

Me too. I think the only clear signal is that we haven't had a straight line cooling to well below average. The fluctuations seen so far will reinforce the hope that December may provide this winter's best chance of colder episodes. It will be interesting to see which way the stratosphere heads after this weeks slight warm up.

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Midweek update is only partial due to the fact that the Berlin Winter diagnostic site seems to have trouble with putting its info on the net - all data forecasts are 'not available' for the last day. Has any one else had any trouble viewing the forecasts?

Otherwise at the 30 hPa level the small warming to average seems to have reversed however at the 10 hPa level the temp is above average but I suspect that this is going to drop soon.

30hpa level

10hpa level

Looking at the temps at the 10 hPa level then it appears that the rise in temp over the North Pole can be explained by the position of the vortex which is centered over Svalbard presently.

The missing Berlin data is useful as it shows the average temp and forecast between the North Pole and 60ºN, not just at the North Pole. Looking at the NCEP forecast charts, they suggest a decrease of the 10hPa temps and an increase in the strength of the polar vortex though these long term forecasts are not the most reliable! However if this was to occur it wouldn't be altogether unexpected due to the westerly QBO and would be an unfavourable jigsaw piece for those hoping for cold weather come January.

c

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Guest zebra danio
Midweek update is only partial due to the fact that the Berlin Winter diagnostic site seems to have trouble with putting its info on the net - all data forecasts are 'not available' for the last day. Has any one else had any trouble viewing the forecasts?

Otherwise at the 30 hPa level the small warming to average seems to have reversed however at the 10 hPa level the temp is above average but I suspect that this is going to drop soon.

30hpa level

10hpa level

Looking at the temps at the 10 hPa level then it appears that the rise in temp over the North Pole can be explained by the position of the vortex which is centered over Svalbard presently.

The missing Berlin data is useful as it shows the average temp and forecast between the North Pole and 60ºN, not just at the North Pole. Looking at the NCEP forecast charts, they suggest a decrease of the 10hPa temps and an increase in the strength of the polar vortex though these long term forecasts are not the most reliable! However if this was to occur it wouldn't be altogether unexpected due to the westerly QBO and would be an unfavourable jigsaw piece for those hoping for cold weather come January.

c

I would go off the ECM predictions. As of yesterday it was showing a sustained level slightly above average out to the 10th. Some cooling is quite likely to follow but that link you show for 30mb will probably show another rise in the meantime as it is a day or two behind the ECM forecast I believe. That will take us out to the second to third week of December anyway.

The other thing to consider is the continued position of the vortex. There are indications of a split with a section of the PV displaced even further eaast towards Siberia (a very good thing for us) and also a very possible CW (Canadian warming) - ie that warmer anomaly over alaska triggering cross polar ridging, which will result in a sector of the PV over Baffin Island lifting out south and east with the consequence that the jet over the USA will be suppressed (take the northern arm spoiler out) and help the NAO go properly negative. It doesn't reverse the west to east polarity of the stratospheric jet normally like a MMW can do but it is sufficient to weaken and displace the vortex and send the jet south for a period,

I'm not sure that even a cool off in the stratosphere by, say, mid month, will affect these prospects for the rest of this month and into the start of Jan, so there is plenty of time for a significant cold spell to evolve over the next 4 - 5 weeks before any cooling and lowering of heights to the north takes effect (if it happens).

If that is a ramp, so be it! :)

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Guest zebra danio
Interesting site which helps to link in Zebra Danio's comments:

Mods. DO feel free to move this post if deemed in the wrong forum.

http://www.stormsurfing.com/cgi/display_alt.cgi?a=natla_250

:doh: da bish

latest berlin update

http://strat27.met.fu-berlin.de/cgi-bin/ti...mps&alert=1

Shows a forecast of slightly above to average conditions persisting out to midmonth. The longer any significant cooling is delayed the more it will assist January when the state of the stratosphere, polar westerlies and impact on AO are at their greatest.

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:lol: da bish

latest berlin update

http://strat27.met.fu-berlin.de/cgi-bin/ti...mps&alert=1

Shows a forecast of slightly above to average conditions persisting out to midmonth. The longer any significant cooling is delayed the more it will assist January when the state of the stratosphere, polar westerlies and impact on AO are at their greatest.

So still a fluctuating forecast without significant below average stratospheric cooling forecast. I agree ,ZD, that the warmer anomaly must have some influence but wasn't sure how so thanks for your informative post explaining how this could occur. I have been expecting the stratosphere to switch back to its recent history of below average cooling and feel that we are in some kind of bonus time until it does so.

To my mind, I think that the strong Greenland tropospheric vortex that has blighted our recent winters will occur, but not until January and this is not taking other factors into account which could possible override the stratospheric influence.

I enjoy reading your posts on the model output thread ZB so please keep them up - a welcome addition to nw's other excellent analytical posters. Fingers crossed for a warmer stratosphere.

c

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Guest zebra danio
So still a fluctuating forecast without significant below average stratospheric cooling forecast. I agree ,ZD, that the warmer anomaly must have some influence but wasn't sure how so thanks for your informative post explaining how this could occur. I have been expecting the stratosphere to switch back to its recent history of below average cooling and feel that we are in some kind of bonus time until it does so.

To my mind, I think that the strong Greenland tropospheric vortex that has blighted our recent winters will occur, but not until January and this is not taking other factors into account which could possible override the stratospheric influence.

I enjoy reading your posts on the model output thread ZB so please keep them up - a welcome addition to nw's other excellent analytical posters. Fingers crossed for a warmer stratosphere.

c

your welcome - great idea of yours to start up this thread and supply some really good background info :lol: . I must admit I find this subject really fascinating and with this thread we can inedeed check progress of temperature trends and see how things pan out with lag effects etc down the line

There is no guarantee of course that even with a relatively warmer stratosphere we will get the influeces we are looking for, but there appear to be quite a few forecasters who still believe that the above described scenario wrt the movement of the vortex could kick start a -NAO and provide a phase of higher latitude blocking. (The atlantic set-up needs to play ball though with less energy off the eastern seeboard)

The 90N reading is the one which I think dictates the strength of the vortex and as long as that stays near average then we can expect a weaker PV than last winter. So January may not be nearly as bad - hence the longer any cooling can be put off the better. However, it is still early days and this relatively warmer trend needs to be sustained. Any corresponding warming in the 30mb level in the short term will assist any chance of height rises later in December so even if there is a cooling soon, there is still a window of opportunity at least till early to mid Jan on present indications. Another wave breaking mountain torque event cannot be ruled out either - which would provide another small boost to hep things along, and that would be very good news.

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I may not contribute much to this thread but I do enjoy reading it.

Some excellent posts today and I must say ZD what a welcome addition you are to this forum.

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I too find the subject of stratospheric warming and cooling a fascinating subject but know a very limited amount about it. Many thanks to Ch and Zd for all their input so far and I will keep reading this particular thread with great interest..

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