Stratosphere Temperature Watch

[karyo]

Looking at the bigger picture, February is not looking great unless we can get a MMW, so a few weeks of less cold weather may well be a price worth paying. A similar situation occurred in the winter of 86/87 after a displacement MMW then.

Chiono, why is February not looking great? I have asked this question in the model output discussion, a few days ago, and nobody came up with a tangible asnwer!

Karyo

[chionomaniac]

Chiono, why is February not looking great? I have asked this question in the model output discussion, a few days ago, and nobody came up with a tangible asnwer!

Karyo

The stratosphere is currently cooler than average with an excess of positive (westerly) wind anomalies. The upwelling seen throughout December and January so far is coming to an end and these positive zonal winds are likely to propagate down and increase the strength of the polar vortex and lead to a positive AO month. Any MMW will hopefully counteract this.

[MR EXTREMES]

pretty sure the next four weeks wont be eventfull in a wintry sense,

but still think end of febuary could be intresting.

the one thing we do have is a neg nao,

ao looks like going + and stratosphere being rather cold.

still chance of change but i think its about run its coarse and would need some kind of special warming in the strat to push things along.

so stuck in a rut at the moment.

[karyo]

The stratosphere is currently cooler than average with an excess of positive (westerly) wind anomalies. The upwelling seen throughout December and January so far is coming to an end and these positive zonal winds are likely to propagate down and increase the strength of the polar vortex and lead to a positive AO month. Any MMW will hopefully counteract this.

Thank you for the reply. Ok, so basically, it is the cold state of the stratosphere.

Let's see whether this forecasted warming materialises and hope it propagates wornwards as quickly as possible.

Karyo

[weatherjunkie]

AyO this looks interesting (please excuse my poor pun). Perhaps another situation where the troposphere counteracts the stratosphere? Or will this change to reflect the strengthening vort and positive mean zonal winds downward propagation?

Edited January 12, 2010 by weatherjunkie

[picog]

The chart you posted weatherjunkie seems to indicate that the AO is going up to around zero for a day or so around Jan 20 before turning potentially very negative again. To me, that looks like good news for the MMW?

[chionomaniac]

The chart you posted weatherjunkie seems to indicate that the AO is going up to around zero for a day or so around Jan 20 before turning potentially very negative again. To me, that looks like good news for the MMW?

I suspect the reason that the AO rises temporarily on the ensembles is due to the reshaping of the vortex and transferring of energy and to eastern Siberia. If one looks at the vortex profile at T+240 we can see a pattern that extends from the troposphere right up into the top layers of the stratosphere. This is caused by the vortex being partially displaced from the pole by the warming that is occurring. Whether we get a full displacement and total collapse of the zonal winds remains to be seen but with the large amplitude wave 1 activity it is looking more likely than not.

The warming is still forecast to occur at lowering levels and looks more significant at the 10hPa level today with the zonal winds reducing accordingly.

One other thing is that there appears to be a recharging of extreme cold at the North Pole and so if the AO does relax and return to negative there will be some extreme cold flooding south.

http://strat-www.met.fu-berlin.de/cgi-bin/ecmwfzm?alert=1&forecast=all&var=t

c

[picog]

I suspect the reason that the AO rises temporarily on the ensembles is due to the reshaping of the vortex and transferring of energy and to eastern Siberia. If one looks at the vortex profile at T+240 we can see a pattern that extends from the troposphere right up into the top layers of the stratosphere. This is caused by the vortex being partially displaced from the pole by the warming that is occurring. Whether we get a full displacement and total collapse of the zonal winds remains to be seen but with the large amplitude wave 1 activity it is looking more likely than not.

The warming is still forecast to occur at lowering levels and looks more significant at the 10hPa level today with the zonal winds reducing accordingly.

One other thing is that there appears to be a recharging of extreme cold at the North Pole and so if the AO does relax and return to negative there will be some extreme cold flooding south.

http://strat-www.met...ecast=all&var=t

c

Thanks chionomaniac — things look encouraging. In your experience, how accurate/reliable are the forecast charts. I get the 'impression' that they are considerably more reliable than weather predictions.

[weatherjunkie]

Today's AO chart.

[chionomaniac]

Very much game on still.

The tropospheric vortex profile is being very much dictated by the stratospheric displacing vortex. Even if we don't get a full MMW the displacement being seen will still have some effect on the troposphere.

Remember the MMW last year. I think that I classified 2 effects felt here at ground level. We initially had a primary effect from the split, followed by a later secondary effect by the vortex collapse. The primary effect was responsible for the February snow and the secondary effect was responsible for dramatically reducing the strength of the jet steam ( no blocking as was expected due to La Nina conditions).

This year any primary effect, that happens with very little delay and is associated with the positioning of the vortex, will be responsible for displacing the vortex towards eastern Siberia. This opens the door for an easterly and whether that actually occurs remains to be seen. This primary effect is likely to be seen whether or not a full MMW takes place or not. Any secondary effect which occurs at a later timeframe up to 6 weeks later will need to be monitored. Theoretically it is in this period that if the vortex has collapsed that there is an increased risk of northern blocking.

c

[chionomaniac]

GFS is in agreement with the ECM over the warming. What is good to see is a substantial warming at the 10 hPa level and also propagation down to the 50 hPa level.

10 hPa level

50 hPa level

This is creating a pronounced effect and distortion of the polar vortex as can be seen here.

When the vortex is completely pushed off the pole we have a MMW. Last year I have looked up and this occurred on the 24th of January. This year I expect provisionally a MMW to occur around 27th January. We shall see. Of course this time we are already seeing benefits of a partially displaced vortex and may reap the benefits sooner than the event.

c

Edited January 13, 2010 by chionomaniac

[BLAST FROM THE PAST]

Interesting. In my method the jetstream is affected by solar and lunar output/phases. We have a peak energy period approaching end of the month and the effect will shove the jetstream northward temporarily, hence the breakdown of the cold and projected stormy spell. I anticipate then a renewed southerly tracking thrust as we enter into Feb. This peak energy period is crucial IMO and where the anticipated deep LP tracks is likely to determine our outcome. I am now seeing good support for Northerly and Ne'ly winds to take us through first half of Feb

BFTP

[cooling climate]

GFS is in agreement with the ECM over the warming. What is good to see is a substantial warming at the 10 hPa level and also propagation down to the 50 hPa level.

10 hPa level

50 hPa level

This is creating a pronounced effect and distortion of the polar vortex as can be seen here.

When the vortex is completely pushed off the pole we have a MMW. Last year I have looked up and this occurred on the 24th of January. This year I expect provisionally a MMW to occur around 27th January. We shall see. Of course this time we are already seeing benefits of a partially displaced vortex and may reap the benefits sooner than the event.

c

This winter we have already seen a major warming event in the stratosphere and a completely displaced vortex.

We have seen a -AO down to a - 6SD and this could not be achived without the above.

Admittedly it looks as though the warming we have seen occurred in the lower levels of the stratosphere (30hpa)

and not a top down as is now being forcast.

[Cecil Hogmanay Melchett]

This winter we have already seen a major warming event in the stratosphere and a completely displaced vortex.

We have seen a -AO down to a - 6SD and this could not be achived without the above.

Admittedly it looks as though the warming we have seen occurred in the lower levels of the stratosphere (30hpa)

and not a top down as is now being forcast.

Well my limited understanding is a 4 to 6 week lag before the effects of any SSW are felt in the atmosphere?

We need something dramatic as pressure is falling over the pole and the PV is setting up shop where we dont want it to.

[chionomaniac]

Well my limited understanding is a 4 to 6 week lag before the effects of any SSW are felt in the atmosphere?

We need something dramatic as pressure is falling over the pole and the PV is setting up shop where we dont want it to.

As I have previously stated the NH winter pattern is going to be dictated by the displacing polar vortex which is forecast to be situated over Eastern Siberia in the coming weeks. The only fly in the ointment is the recent cold stratosphere which has caused an increase in positive (westerly) mean zonal winds. These are now propagating down to the troposphere and increasing the polar vortex which is why the models are leaving enough strength in the Greenland segment to suggest that the troughing here may prevent westward movement of the large Siberian High. We shall have to wait and see.

The cold stratosphere that is that fly in the ointment looks to be coming to an end though.

The latest ECM forecast is suggesting reversal of the mean zonal winds at the 1hPa level as the wave 1 induced warming continues.

This has been caused by a displacement of the polar vortex at that level:

The programmed warming continues to be forecast to propagate down to lower levels of the stratosphere which is important if we are to see a MMW:

c

[bluearmy]

the extended ens NAEFS, are now consistently showing the blocking transferring back to our nw in the longer term with the trough headed slowly east and just about getting past the meridian by the end of the month. i wonder how an MMW will affect this? i have a feeling we need to get rid of this siberian/asian block - its a long long time since its done us any good and it could end up creating a west based -NAO with us stuck in no mans land or worse still, the warm side of the trough.

[cooling climate]

This looks encouraging also.

Edited January 14, 2010 by cooling climate

[chionomaniac]

the extended ens NAEFS, are now consistently showing the blocking transferring back to our nw in the longer term with the trough headed slowly east and just about getting past the meridian by the end of the month. i wonder how an MMW will affect this? i have a feeling we need to get rid of this siberian/asian block - its a long long time since its done us any good and it could end up creating a west based -NAO with us stuck in no mans land or worse still, the warm side of the trough.

I agree regarding the block, ba. I don't think that we need to get rid of it completely, but in it's present state it is asking a lot to throw a ridge far enough westwards to reach the UK, and even when this does occur the deep cold has a long way to travel before it reaches us and it may be asking a bit too much. I would like to see a segment break off the block and travel westwards with troughing digging in behind - but I ask is this really likely with the forecasted displacement over eastern Siberia? The 6Z GFS hints at this out of nowhere so I guess we can't rule it out. If blocking does occur following the MMW then I doubt it would be immediate and we would have to be patient - February at the earliest but I will keep watching those zonal wind forecasts. Any possible MMW will be totally different to last years and completely different to the tropospheric splitting with have seen this winter so far.

Oh and these blocking forecasts don't suggest strong Greenland PV either:

Edited January 14, 2010 by chionomaniac

[Guest North Sea Snow Convection]

It's quite possible that the block might sit to our north east, and then pending potential eventual reversal of zonal winds once again (after propagation of the warming) then the block can retrogress westwards.

So I'm not sure that we want rid of it at all. It will keep a very handy cold pool up there plus the big snow cover feedback loop that has definitely served the intense -AO we have seen this winter up to now so well.

Edited January 14, 2010 by North Sea Snow Convection

[picog]

Interesting. In my method the jetstream is affected by solar and lunar output/phases. We have a peak energy period approaching end of the month and the effect will shove the jetstream northward temporarily, hence the breakdown of the cold and projected stormy spell. I anticipate then a renewed southerly tracking thrust as we enter into Feb. This peak energy period is crucial IMO and where the anticipated deep LP tracks is likely to determine our outcome. I am now seeing good support for Northerly and Ne'ly winds to take us through first half of Feb

BFTP

Does the peak energy you refer to BFTP, relate to the phase of the moon, sun spot numbers or something completely different? If a minimum energy period occurs (when might this be?), does it influence the jet stream to take a more southerly route?

[Duane S.]

Quick question to those in the know. What exactly constitutes a MMW event?

Is it when the prevailing winds in the Stratosphere literally reverse (as opposed to slow down)?? If so at what level is this taken from?

[chionomaniac]

Quick question to those in the know. What exactly constitutes a MMW event?

Is it when the prevailing winds in the Stratosphere literally reverse (as opposed to slow down)?? If so at what level is this taken from?

Hi s4lancia

A major mid-winter warming is defined to occur when the zonal mean zonal winds at 60N and 10hPa become easterly during winter (NDJFM). The first day on which the daily mean zonal mean zonal wind at 60N and 10hPa is easterly is defined as the central date of the warming. No day within 20 days of the central date can also be defined as a warming. Finally, it is important to highlight that only mid-winter warmings are considered here. To ensure this, cases where the zonal mean zonal winds become easterly but do not return to westerly for at least 10 consecutive days before the 30th April are assumed to be final warmings, and as such are discarded.

Definition from here: http://www.columbia.edu/~lmp/paps/charlton+polvani-JCLIM-2007.pdf

[Duane S.]

Hi s4lancia

A major mid-winter warming is defined to occur when the zonal mean zonal winds at 60N and 10hPa become easterly during winter (NDJFM). The first day on which the daily mean zonal mean zonal wind at 60N and 10hPa is easterly is defined as the central date of the warming. No day within 20 days of the central date can also be defined as a warming. Finally, it is important to highlight that only mid-winter warmings are considered here. To ensure this, cases where the zonal mean zonal winds become easterly but do not return to westerly for at least 10 consecutive days before the 30th April are assumed to be final warmings, and as such are discarded.

Definition from here: http://www.columbia.edu/~lmp/paps/charlton+polvani-JCLIM-2007.pdf

Thanks Chionomaniac, a great explanation.

[chionomaniac]

Hmm, latest forecasts are suggesting that even though there is a temporary reversal of zonal winds at the 1 hPa level that this is not carried through to the 10 hPa level before temperatures start to cool again. So no MMW. However the vortex does displace significantly in this process but I would fear that there will be no full collapse of zonal winds. This forecast will need to be monitored as the amplitude of wave 1 is still set to rocket and I have seen this kind of uncertainty at the FI range before.

http://strat-www.met.fu-berlin.de/cgi-bin/times?plot=all&alert=1

If one looks here at the zonal wind profile it is clear to see what happens to the polar vortex as the warming occurs. If you trace the charts down one can see that the strong westerly winds (orange colour) reduce in intensity before being replaced at the upper levels of the stratosphere by strong easterly winds (blue colour). The strength of the reversal at the upper levels does suggest to me that the forecasts could change regarding a MMW as propagation occurs. I feel that the disruption of the vortex will still have tropospheric effects ( Note the easterly tropospheric polar winds at T+192) but these affects may not be in area that we will benefit from.

http://strat-www.met.fu-berlin.de/cgi-bin/ecmwfzm?alert=1&forecast=all&var=u

Still a very interesting period of model watching both stratospherically and tropospherically.

c

[brogdale]

Hmm, latest forecasts are suggesting that even though there is a temporary reversal of zonal winds at the 1 hPa level that this is not carried through to the 10 hPa level before temperatures start to cool again. So no MMW. However the vortex does displace significantly in this process but I would fear that there will be no full collapse of zonal winds. This forecast will need to be monitored as the amplitude of wave 1 is still set to rocket and I have seen this kind of uncertainty at the FI range before.

http://strat-www.met...lot=all&alert=1

If one looks here at the zonal wind profile it is clear to see what happens to the polar vortex as the warming occurs. If you trace the charts down one can see that the strong westerly winds (orange colour) reduce in intensity before being replaced at the upper levels of the stratosphere by strong easterly winds (blue colour). The strength of the reversal at the upper levels does suggest to me that the forecasts could change regarding a MMW as propagation occurs. I feel that the disruption of the vortex will still have tropospheric effects ( Note the easterly tropospheric polar winds at T+192) but these affects may not be in area that we will benefit from.

http://strat-www.met...ecast=all&var=u

Still a very interesting period of model watching both stratospherically and tropospherically.

c

Yes, still interesting and still with the potential to surprise us

For the benefit of any followers of this thread who are not able to see the Strat thread on TWO I thought I'd post an edited version:-

As the cold spell receeds (temporarialy?) some may start to look for factors capable of bringing some more winter weather, so I thought I'd attempt a Strat update.

Outwardly the signs for a SSW(MWW) event may look encouraging from this data:-

http://strat-www.met.fu-berlin.de/cgi-bin/times?plot=temps&alert=1

with NH strat temps forecast to rise quite steeply in the near future.

But there are few signs that this warming, even if it did develop into a definable SSW, would be one that significantly affected the zonal winds of the Trop; ie. I suspect it would not become a downward propagator.

I base this assertion on findings outlined in this piece from two Japanese researchers, that attempts to establish why some SSW events propagate downwards to affect the troposphere and others don't.

http://center.stelab...mazaki_koji.pdf

Nakagawa & Yamazaki highlight we need to be looking out for if we hope to see a Splitting SSW capable of driving some cold our way later in the season is the following:-

a) Increasing Wave 2 energy flux

B) Less strong wave 1 energy

c) Poleward EP flux

d) Decreasing zonal wind velocity in the high trop.

http://acdb-ext.gsfc.nasa.gov/Data_services/met/metdata/annual/z2n_50_2009.pdf showing the Wave 2 energy flux to be fairly unexceptional this year (red), certainly compared with the massive peaks that hepled to precipitate last year's event (blue)

http://acdb-ext.gsfc.nasa.gov/Data_services/met/metdata/annual/z1n_50_2009.pdf showing significantly high Wave 1 flux (red) which, according to the Japanese, is unhelpful to propagation ( and note last January's much lower values in blue)

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/html_e/ep_12z_nh.html showing some healthy flux up into the Strat, but with very little of the poleward component associated with propagator type.

http://acdb-ext.gsfc.nasa.gov/Data_services/met/metdata/annual/u60n_150_2009.pdf showing (in blue) last years 'textbook' dramatic rise, then fall in high trop zonal winds either side of the key day (point of max warming @10 hPa). This year's red line does not show that pattern.

I'm afraid therefore that the current state of play does not really indicate that we're in for another whopping (splitter) SSW(MWW), nor do I think that any event that did occur would significantly affect the Trop. Sorry to report that, and i hope really that i may be proved wrong, but I think we may well have to look elsewhere this year for the cause of our next cold spell. Lack of SSW doesen't seem to have hindered us thus far