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chionomaniac

Stratosphere Temperature Watch

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Every winter the temperature of the stratosphere above the North Pole to around 60 N cools rapidly. This cooling is influenced by strong cyclonic winds and has an affect on the troposphere below, which in turn influences our own weather. The greater the cooling in the stratosphere, the stronger the polar vortex in the troposphere. This has the affect of creating a more positive AO which leaves us experiencing milder wetter winters driven along by westerly winds. A less cool stratosphere will ultimately lead to a more negative AO and cooler, dryer winter weather.

post-4523-1225615445_thumb.jpg

Effects of the Positive Phase | Effects of the Negative Phase

of the Arctic Oscillation of the Arctic Oscillation

(Figures courtesy of J. Wallace, University of Washington)

Occasionally the stratosphere can undergo dramatic warming events. These occur when the cyclonic winds at around 60N slow down suddenly, halt or even reverse.

http://en.wikipedia.org/wiki/Sudden_stratospheric_warmings

This can have the affect of disrupting the polar vortex underneath (up to 6 weeks later) and creating a very negative AO with polar air flooding southwards. These are of obvious interest to us because it can create very cold conditions for us. A recent example of a Sudden Stratosphere Warming was at the end of Feb 2008. Remember the cold around 6th April around 6 weeks later.

The following link gives the 30hp monthly mean North Pole temps since 1955. Interestingly figures are given for cold monthly means at the bottom of the table. These are temps I would like the stratosphere to avoid this upcoming winter!

http://www.geo.fu-berlin.de/en/met/ag/stra...pole/index.html

The idea of this thread is so that we can monitor the temps in the stratosphere over the upcoming winter. The data can be found here:

http://www.cpc.ncep.noaa.gov/products/stra...ere/strat-trop/

And here:

http://strat-www.met.fu-berlin.de/cgi-bin/diagnostics?1

Below is a chart showing the above or below average cooling around the north pole at the moment. The green is indicating that temps around now at that level of the atmosphere are cooler than average.

post-4523-1225617439_thumb.png

And below is the wind anomaly chart over the north pole. This shows that there are around average winds at present:

post-4523-1225617716_thumb.png

The full reasoning around why Sudden Stratosphere Warmings occur are complex and multifactorial. GP, the NW teleconnections guru has probably one of the best understandings in this field. He has suggested in the past that intense tropical convection in the Indian Ocean leads to powerful downstream anticyclones. This creates fast Rossby Wave Dispersal events which, if allied to a weak zonal wind anomaly, are a precursor to stratospheric warming events. The intense tropical convection is triggered by above average SSTs in that area.

Further info from: http://www.appmath.columbia.edu/ssws/index.php

Also current cooling graph:

post-4523-1225618573_thumb.png

And forecast: http://strat-www.met.fu-berlin.de/cgi-bin/...mps&alert=1

Heres to a warm stratosphere this winter.

c

Further link: http://www.atmosphere.mpg.de/enid/2__Ozone/-_Cooling_nd.html

Ps any other info / thoughts welcome on a subject I am trying to get to grips with!

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Great post for the winter months to come!

But first for me and everyone to come can you please explain some thing a little more?

The greater the cooling in the stratosphere, the stronger the polar vortex in the troposphere.

How does that happen? Please explain the mechanism by which this happens.

Here's my guess.

A cooler stratosphere is more dense, and squeezes down toward the Earth onto the troposphere below. This pressure is released in the troposphere in the form of more intense cyclonic activity. I know the troposphere above the poles is thinner than elsewhere on Earth so could be susceptible to this.

If this is correct that would mean the cold stratosphere presses down and 'traps' the cold at the poles. But when a warming event occurs, the pressure is released and the cold can escape to lower latitudes.

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The full reasoning around why Sudden Stratosphere Warmings occur are complex and multifactorial. GP, the NW teleconnections guru has probably one of the best understandings in this field. He has suggested in the past that intense tropical convection in the Indian Ocean leads to powerful downstream anticyclones. This creates fast Rossby Wave Dispersal events which, if allied to a weak zonal wind anomaly, are a precursor to stratospheric warming events. The intense tropical convection is triggered by above average SSTs in that area.

One of several causes falling into three main categories:-

Rossby Wave Dispersal from anticyclones;

Planetory wave breaking from strong mountain torques associated with increased storminess over the mountain ranges of the hemisphere;

Imbalances in stratospheric ozone over the pole associated with anomalous Brewer-Dobson circulations.

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Great post for the winter months to come!

But first for me and everyone to come can you please explain some thing a little more?

How does that happen? Please explain the mechanism by which this happens.

Here's my guess.

A cooler stratosphere is more dense, and squeezes down toward the Earth onto the troposphere below. This pressure is released in the troposphere in the form of more intense cyclonic activity. I know the troposphere above the poles is thinner than elsewhere on Earth so could be susceptible to this.

If this is correct that would mean the cold stratosphere presses down and 'traps' the cold at the poles. But when a warming event occurs, the pressure is released and the cold can escape to lower latitudes.

Truth is AF, I don't really know!

My take on it is slightly different - it could be right - it could be wrong - if someone here knows better I am willing to learn. I reckon that the winter default stratosphere pattern is a strong cold vortex similar to a spinning top. This spinning top will try and reach maximum speed but is prevented from doing so by intrinsic stratospheric friction and friction from the stratosphere radiating towards the equator. This friction generates a certain amount of heat. The vortex itself encourages the troposphere polar vortex below in a way as if a hoover nozzle was sucking from above. The statospheric vortex can also be interfered with from extrinsic factors such as those that GP mentions in his post above. These factors have the effect similar to putting a stick in the spoke of a wheel generating a sudden stratospheric warming event. I don't know whether it is the warming or the stopping of the wheel that affects the troposphere below, but I reckon it has the affect of turning the hoover off and the tropospheric polar vortex spins itself out, leaving pressure rises in the polar regions and a negative AO. I could be totally wrong though!

Regards

c

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I know that under HP air is sinking and under LP air is rising so how that interlinks with the stratosphere I really don't know.

I know that as winter approaches ozone levels change and the stratosphere tends to cool hence the likelihood of the PV. Obviously it is the 'norm' so needs a strong influence to take it away.

BFTP

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The full reasoning around why Sudden Stratosphere Warmings occur are complex and multifactorial. GP, the NW teleconnections guru has probably one of the best understandings in this field. He has suggested in the past that intense tropical convection in the Indian Ocean leads to powerful downstream anticyclones. This creates fast Rossby Wave Dispersal events which, if allied to a weak zonal wind anomaly, are a precursor to stratospheric warming events. The intense tropical convection is triggered by above average SSTs in that area.

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This might be worth watching...

-ve zonal anomalies @ 30 hPa should allow for ozonolysis and warming at that layer off-setting any cooling effects thus far.

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Stratospheric warmings quite often reflect the displacement of the stratospheric vortex or the splitting of the vortex. GP is right about the causes but not all Rossby Wave Dispersal , planetary wave breaking etc cause a warming. This depends of the strength of the event, what direction the QBO is in and the strength and location of the vortex.

You should note that the stratospheric vortex usually starts up over Siberia and northern canada before migrating north. The siberian origin vortex usually dominates, but may wobble away from the north for periods before moving back over siberia and decaying. This is why the spring snow melt time in siberia, the amount of rain across the continental interior during summer play a role in the time of the stratospheric vortex start up time. I have no evidence yet to link vortex start up time to propensity for the vortex to wobble away from the pole, but I have a suspicion this may be true. This could perhaps suggest a wet UK summer (dry continental summer) is an indicator for winter weather. I would however point out that low planatary angular momentum conditions are not normally condusive to the kind of strong events that would trigger a warming (strong anticyclones perhaps being the exception).

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There might be some data issues here....but....

http://ds.data.jma.go.jp/tcc/tcc/products/...e/pole30_n.html

DWD/ECM site not so warm

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

NOAA zonals tells us why there might be some warming here, less fast moving air will be subject to formation of ozone and release of heat energy = warming

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

and some suggestion of average, possibly trending upwards on the temperature front

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

So we will have to wait a day or two to get confirmation on whether an early season warm event is underway, I suspect not as strong as being shown by the Japan site alhough there is logic behind some degree of warming, both in terms of zonal winds and what happend last month over the tropics.

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yes, data issue perhaps with that first link GP, UNLESS something is afoot. Its certainly the largest change, up or down, for quite some time, if it is correct. As you say we need to wait a few days to see if its sustained.

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Both the ECM and Japan models look similar for 3rd Oct

post-4523-1225876151_thumb.png

post-4523-1225876182_thumb.png

so certainly something to watch.

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How significant is the position of the stratospheric warm anomaly? Do we want it near us?

BTW thanks chionomaniac for your explanation of what causes the polar vortex.

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How significant is the position of the stratospheric warm anomaly? Do we want it near us?

I don't know the answer to that ( but would like to!). What I do know though, is that the warm anomoly is forecast to migrate east over Alaska, and reduce in intensity.

post-4523-1225920982_thumb.png

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I've just read John's LRF from 5 Nov and was intruiged by the last sentence. Thought I'd post here to bring the topic up the page. I really think that stratospheric warming will play a big part this winter and hope the more experienced/knowledgeable members can keep us updated.

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I've just read John's LRF from 5 Nov and was intruiged by the last sentence. Thought I'd post here to bring the topic up the page. I really think that stratospheric warming will play a big part this winter and hope the more experienced/knowledgeable members can keep us updated.

Don't worry GP is keeping a close eye on this. The stratospheric temperatures have jumped to well above normal. Even with the drop yesterday, the temperature is still above normal so let's hope that this continues especially with the negative wind anomalies over the North Pole, as GP explained yesterday.

Hopefully we'll see the results of this when it really matters (around December)!

Karyo

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Hopefully we'll see the results of this when it really matters (around December)!

Karyo

As I understand things, and I may be wrong, there is a 6 week delay in response to a warming event, so with the stratospheric warming that occurred on the 4th, it should equate to favourable synoptics around the middle of December.

We should also look to the warming lasting for, oh, around 3 months :doh: !!

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and the reason I said this

On a separate note, the 30mb temperature curve has just taken an sudden upward surge. I'm not sure if this is a data problem or a genuine indication. In any case it will be late November before any effects, at the earliest, would be felt from this.

and suggested caution, even if it was, as it now appears, genuine, is there for all to see today.

Its fallen almost as many degrees as it rose at the time I wrote my lrf.

Do beware of any individual item/link/teleconnection, call them what you like, they are ALL subject to change which no one, least of all me, is really able to predict.

GP may correct me but I would think that any warming needs to last for several days at least to have any real impact on n hemisphere weather?

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at the earliest, would be felt from this.

I would think that any warming needs to last for several days at least to have any real impact on n hemisphere weather?

Obviously GP knows a lot more about this, but in February we saw similar sharp and short stratospheric warming events that led/contributed to the cold spells we experienced in March and April. It was a case of one happening after the other, so i think all eyes should be on the stratospheric temperature link in the coming days!

http://ds.data.jma.go.jp/tcc/tcc/products/...e/pole30_n.html

Karyo

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The event in February was far greater. Firstly the stratospheric wind anomaly was great enough to reverse the polar winds as shown below:

post-4523-1226079511_thumb.png post-4523-1226079995_thumb.png

This time the reduction in stratospheric vortex is not strong enough to reverse.

The net result is that the warming event in Feb was strong enough to filter right down to the tropopause layer. The present warming hardly takes us above average so not of major significance as of yet:

post-4523-1226079846_thumb.png

c

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am i right in assuming prolonged cold snaps can still occur without stratospheric warming?

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best you ask GP that question as I have no data on it

The event in February was far greater. Firstly the stratospheric wind anomaly was great enough to reverse the polar winds as shown below:

post-4523-1226079511_thumb.png post-4523-1226079995_thumb.png

This time the reduction in stratospheric vortex is not strong enough to reverse.

The net result is that the warming event in Feb was strong enough to filter right down to the tropopause layer. The present warming hardly takes us above average so not of major significance as of yet:

post-4523-1226079846_thumb.png

c

thanks for that C, can you give the link to obtaining older data please?

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best you ask GP that question as I have no data on it

thanks for that C, can you give the link to obtaining older data please?

Just lost a post!!!

To azores . The best chances of prolonged cold are with a negative AO( interlinked with a negative NAO). The AO is more likely to be negative with a warmer stratosphere. So whereas a warmer stratopsphere is not essential it is an important building block to help.

You can compare previous cold winter spells to the average winter polar months stratospheric temps which can be found below (since 1955)

http://www.geo.fu-berlin.de/en/met/ag/stra...pole/index.html

Also NOAA data here

http://www.cpc.ncep.noaa.gov/products/stra...ere/strat-trop/

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Just lost a post!!!

To azores . The best chances of prolonged cold are with a negative AO( interlinked with a negative NAO). The AO is more likely to be negative with a warmer stratosphere. So whereas a warmer stratopsphere is not essential it is an important building block to help.

You can compare previous cold winter spells to the average winter polar months stratospheric temps which can be found below (since 1955)

Also NOAA data here;

http://www.cpc.ncep.noaa.gov/products/stra...ere/strat-trop/

http://www.geo.fu-berlin.de/en/met/ag/stra...pole/index.html

current conditions not looking too favourable then! :)

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