Stratosphere temperature watch - 2016/17

[Gael_Force]

6 minutes ago, Frostbite1980 said:

But if the PV was displaced to Scandinavia for example could this not potentially promote HLB over Greenland drawing in N/NE winds over the UK. Not trying to be funny just trying to get to grips with all possibilities.

You'll not need to wait long to test that theory but I don't see an up wave train to Greenland to promote WAA for blocking in the region. 

[Singularity]

GFS zonal bias may well be hurting its stratospheric projections, with this accentuated by the supposedly wayward decaying MJO signal.

Displacements typically send the vortex to either Siberia or N. America - for reasons I've yet to read into the continental landmasses seem to attract the vortex, perhaps due to less modification of deep cold airmassses by the surface - and either way you tend to see the cold air initially follow suit and then on some occasions the vortex stretches back across the Arctic and cold air races across to the opposing side of the hemisphere as a result of the cross-polar flow.

For Europe to go notably cold from a displacement, the vortex needs to be pushed particularly far from the pole such that it ends up entirely within the Eurasian continent; more often the vortex only gets as far as the north slope of Siberia.

Splits tend to work out far better for us because the two separate vortices tend to be weaker and displace further from the Arctic, while in between you see a major height rise with corresponding extensive high-latitude blocking. Many configurations of that bring significant cold weather western Europe and only a few less as far as the UK, but there are still some which can leave us on the benign or even balmy side, annoyingly enough. At least we won't have to tear our hair out over those kind of fine margins this season, assuming nothing highly unexpected takes place 

Edited January 25, 2017 by Singularity

[Weather-history]

11 hours ago, s4lancia said:

Does make you wonder though what would have been if we'd have had the E-QBO that by rights should have been with us this winter...

 

I thought I read that sometimes a strong E QBO is not favourable? Might be wrong

[mountain shadow]

51 minutes ago, karyo said:

No, even with a split it can be unfavourable for the UK. Similar to the displacement it depends where the split occurs. For example you can have a split but with some residual low remaining in the Atlantic side and the UK in a southerly flow. Nothing is guaranteed.

It is more probable with a split than with a displacement, that is what I was alluding too.

[iapennell]

2 hours ago, Weather-history said:

I thought I read that sometimes a strong E QBO is not favourable? Might be wrong

@Weather-history; A strongly easterly QBO is a store of much easterly Atmospheric Angular Momentum (AAM) that is high over the Equator which, by it's nature, will annul the (predominantly) Westerly AAM of the atmosphere from the stratosphere downwards and from Equator to the Poles. It is this westerly AAM which, as it moves to higher latitudes and increases (due to the Coriolis Effect) that powers the Circumpolar Vortex that- in turn- results in a healthy westerly flow off the North Atlantic in most winters. Anything that removes the Westerly AAM of the atmospheric circulation in the Northern Hemisphere- and a large mass of air travelling at speed in the opposite direction high over the Equator (and slowly descending) will lead to the loss of Westerly AAM in the Northern Hemisphere circulation as a whole as the QBO air mixes into the general global atmospheric circulation- would lead to a weakening of the (normally strong) Circumpolar Vortex in higher latitudes in the autumn/winter months.

Whilst the QBO is an important factor in determining the strength of the Circumpolar Vortex (and in turn the likelihood of high-latitude blocking in winter that could bring cold weather to the UK) it is certainly not the only matter. The sunspot and solar-flare activity of the Sun have a significant impact, lots of solar activity- leading to geomagnetic storms results in forces on our atmosphere- through the interaction with Earth's Magnetic Field to increase the intensity of depressions in high latitudes (by reducing thickness heights aloft near the North Magnetic Pole). This leads to an increase in the strength of the Circumpolar Vortex. What you need for blocking, therefore, is a very quiet Sun that does not emit magnetic influences leading to a stronger Polar Vortex.

ENSO neutral and weak La-Nina conditions in the tropical Pacific are also favourable to high-latitude blocking that could bring about cold winter weather to Britain because then the NE Trade Winds over the North Pacific are not going to be too strengthened by an Intertropical Convergence Zone (ITCZ) intensified by the unusually hot Equatorial Pacific surface waters that characterise strong El Ninós :Stronger NE Trade Winds caused by El Ninó heating the Equatorial Pacific and strengthening the ITCZ causes the Northern Hemisphere atmospheric circulation to gain Westerly AAM through frictional interaction of stronger NE Trade Winds with the underlying surface (and fed by the resultant stronger Hadley Cell aloft) and this extra Westerly AAM leads to a strengthening of the Circumpolar Vortex. Weak La Niná or ENSO-neutral conditions in the Equatorial Pacific thus lead to weaker Westerlies in higher latitudes and a higher chance of blocking highs occurring in high latitudes: The very strong El Ninó late 2015 combined with the Westerly QBO were undoubtedly factors contributing to the exceptionally wet mild and south-westerly dominated November and December of 2015.

Surface conditions, and I include the atmospheric temperature variations from the Arctic to mid-latitudes, are also very important with regards to the likelihood of winter high-latitude blocking and cold over Britain. Conditions well upwind as regards the favourability of cyclogenesis are very important, as too are the latitude zones in which such cyclogenesis is encouraged. A strong atmospheric temperature gradient between very cold and frigid air-masses over the Arctic and a warm North Atlantic will promote intense baroclinicity (atmospheric temperature/pressure gradient that promotes depression-formation) and this will lead to strong Westerlies heading towards the UK. However, if the Central Arctic (not the fringes) is unusually warm and the North Atlantic unusually cold this will weaken the temperature-gradient promoting Westerlies and high-latitude blocking (most likely over locations that have surface air still well below freezing despite a warm Central Arctic) becomes a real possibility.

This winter has been much drier than last simply because the warmth of the far North Atlantic and reduced extent of Arctic pack-ice has encouraged a northwards shift in the storm tracks (which tend to follow the strongest atmospheric temperature gradients). The absence of a strong El Ninó is also a contributing factor. However, these Westerlies have still been strong enough over/just north of northern Britain to act as a barrier keeping Arctic air from spilling southwards (or south-westwards from Russia) for the vast majority of time. On the other hand, if the North Atlantic were unusually cold the temperature gradients would shift to lower latitudes and with depressions moving east in the latitudes of the Mediterranean the Westerlies would tend to miss the UK and this country would stand to gain much colder airstreams from north or east in winter.

A number of factors working together are needed to ensure we have prolonged spells with northerly or easterly winds bringing severe cold spells in the winter months to this country. A strongly Easterly QBO over the autumn preceding the winter in question helps but it is not enough by itself (a number of winters in the 1990's and 2000's had these Easterly-QBO conditions yet were mild or average). If, in addition to a strongly Easterly QBO (mean speed over preceding months over 20 m/s from the east), one also has a very quiet Sun, a really cold North Atlantic, ENSO-neutral or weak La Niná in the Equatorial Pacific, unusual warmth over far NE Canada but entrenched cold over Eurasia then one stands a much better chance of getting very cold winter weather.

I hope that this helps with your query.    

Edited January 25, 2017 by iapennell

[bluearmy]

No tech SSW on ec yesterday and more notably, a less marked neg flow higher up which allows the vortex at the very top to begin to reform over scandi

 

[Paul_1978]

How's thing looking for the SSW this morning? Last I read was that the ECM was up for it but the GFS wasn't. 

Also, that the SSW was due to kick in around 29th Jan, which is in 3 days.

Whats the latest?

[Due South]

11 hours ago, iapennell said:

A number of factors working together are needed to ensure we have prolonged spells with northerly or easterly winds bringing severe cold spells in the winter months to this country. A strongly Easterly QBO over the autumn preceding the winter in question helps but it is not enough by itself (a number of winters in the 1990's and 2000's had these Easterly-QBO conditions yet were mild or average). If, in addition to a strongly Easterly QBO (mean speed over preceding months over 20 m/s from the east), one also has a very quiet Sun, a really cold North Atlantic, ENSO-neutral or weak La Niná in the Equatorial Pacific, unusual warmth over far NE Canada but entrenched cold over Eurasia then one stands a much better chance of getting very cold winter weather. 

Can we have this stored, and brought out each autumn. Great post, and would make it a little easier for those like myself, who don't have the knowledge of you guy's.

[chris55]

No official SSW on the ECM from yesterday. A reversal at 1hpa and a slackening of zonal winds further down, but the displacement of the vortex not looking like it will end up favouring any HLB in our vacinity. 

We can see more warm air being injected at the pole at day 9/10 so perhaps this may be the second phase as suggested by Ian a few days back.

we really do need to see a split or complete destruction of the strat PV if a direct link to the troph pattern will benefit us regarding some high lay blocking.

[Summer Sun]

 

[Nick F]

^^^ Yep, certainly close but no cigar for a SSW on yesterday's Berlin charts, if anything less likely then previous days, still could happen by end of month, but PV surely weakened and primed for another SSW in Feb perhaps when wave 1 warming and  favourable phase of MJO propagation combine. But I'd much rather see a split rather than displaced sPV - as split more likely to encourage HLB. But as Matt says, we need wave 2 activity to do the split

Edited January 26, 2017 by Nick F

[Interitus]

15 hours ago, iapennell said:

A strongly easterly QBO is a store of much easterly Atmospheric Angular Momentum (AAM) that is high over the Equator which, by it's nature, will annul the (predominantly) Westerly AAM of the atmosphere from the stratosphere downwards and from Equator to the Poles. It is this westerly AAM which, as it moves to higher latitudes and increases (due to the Coriolis Effect) that powers the Circumpolar Vortex that- in turn- results in a healthy westerly flow off the North Atlantic in most winters. Anything that removes the Westerly AAM of the atmospheric circulation in the Northern Hemisphere- and a large mass of air travelling at speed in the opposite direction high over the Equator (and slowly descending) will lead to the loss of Westerly AAM in the Northern Hemisphere circulation as a whole as the QBO air mixes into the general global atmospheric circulation- would lead to a weakening of the (normally strong) Circumpolar Vortex in higher latitudes in the autumn/winter months.

A number of factors working together are needed to ensure we have prolonged spells with northerly or easterly winds bringing severe cold spells in the winter months to this country. A strongly Easterly QBO over the autumn preceding the winter in question helps but it is not enough by itself (a number of winters in the 1990's and 2000's had these Easterly-QBO conditions yet were mild or average). If, in addition to a strongly Easterly QBO (mean speed over preceding months over 20 m/s from the east), one also has a very quiet Sun, a really cold North Atlantic, ENSO-neutral or weak La Niná in the Equatorial Pacific, unusual warmth over far NE Canada but entrenched cold over Eurasia then one stands a much better chance of getting very cold winter weather.   

Since 1948 there are 11 Autumns with average 30mb QBO < -20 and they are followed by winter CET average of 4.58°C

The remaining 57 Autumns were followed by winter CET average of 4.29°C

The winters were (with DJF CET values) -

2005 4.4 4.3 3.7

2007 4.9 6.6 5.4

2014 5.2 4.4 4.0

2012 4.8 3.5 3.2

1974 8.1 6.8 4.4

1979 5.8 2.3 5.7

1996 2.9 2.5 6.7

1970 4.3 4.5 4.5

1972 5.8 4.5 4.3

2003 4.8 5.2 5.4

1984 5.2 0.8 2.1

The interaction between QBO and stratosphere vortex is not as simple as horizontal wind shear or momentum flux. For example, in the paper Interannual Changes of Stratospheric Temperature and Ozone: Forcing by Anomalous Wave Driving and the QBO (Salby 2011)  http://journals.ametsoc.org/doi/pdf/10.1175/2011JAS3671.1 a comparison of modeling and observation shows that

Quote

During early winter, anomalous temperature and ozone are accounted for almost entirely by anomalous EP flux from the troposphere, as they are in the observational record. During late winter, both mechanisms are required to reproduce observed anomalies. Although the QBO forces anomalous structure equatorward of 40°N, the strong anomaly over the Arctic follows principally from anomalous upward EP flux

The explanation is quite complicated but described clearly -

Quote

The residual circulation is driven by planetary waves that transmit momentum upward from the troposphere. When absorbed, that momentum drives a poleward drift, which converges at high latitude to force mean downwelling. The accompanying adiabatic warming maintains Arctic temperature as warmer and the polar-night vortex as weaker than each would be under conditions of radiative equilibrium. Compensating that vertical motion at lower latitudes is mean upwelling, which is accompanied by adiabatic cooling. Simultaneously, the poleward drift transfers ozone rich air from its chemical source at low latitude into the winter hemisphere, where total ozone increases during winter by as much as 100%

These consequences of the residual circulation are closely related to planetary wave activity, which transmits momentum upward from the troposphere. Measured by the net upward Eliassen–Palm (EP) flux near the tropopause Fz, the momentum delivered to the middle atmosphere during winter is determined chiefly by planetary wave structure in the troposphere. An intensification of tropospheric planetary waves leads to anomalous upward EP flux, which, upon being absorbed in the middle atmosphere, forces intensified residual mean motion. In concert with intensified isentropic mixing by planetary waves, those conditions favor a polar-night vortex that is anomalously warm and weak.

Conversely, a weakening of tropospheric planetary waves favors a polar-night vortex that is anomalously cold and strong. A similar influence is exerted by the quasi-biennial oscillation (QBO) of stratospheric equatorial wind uEQ. By displacing the critical line of planetary waves, the QBO controls where in the middle atmosphere EP flux is absorbed and, hence, where residual mean motion is forced (Holton and Tan 1980; McIntyre 1982).

During QBO easterlies, the critical line and mean meridional motion are advanced into the winter hemisphere, along with downwelling and adiabatic warming. Those conditions favor a polar-night vortex that is anomalously warm and weak, with increased wintertime ozone (Gray and Pyle 1989; O’Sullivan and Salby 1990; O’Sullivan and Young 1992; Tung and Yang 1994). During QBO westerlies, the critical line and mean meridional motion are removed into the summer hemisphere. Those conditions favor a polar-night vortex that is anomalously cold and strong, with reduced wintertime ozone.

Jointly, changes of upward EP flux from the troposphere and of equatorial wind associated with the QBO represent anomalous forcing of the residual circulation. They drive an anomalous residual circulation, one that modulates climatological-mean residual motion. Implied are commensurate changes of wintertime temperature and ozone. Augmenting these dynamical influences are sporadic influences from volcanic eruptions and ENSO, as well as the solar cycle. For interannual changes collected over several decades, however, the latter (if only because they are infrequent or cyclical) are secondary to the influences of EP flux and the QBO. Indeed, observed forcing of the residual circulation bears a close relationship to observed changes of the polar-night vortex, as well as to changes of Northern Hemisphere ozone (Fusco and Salby 1999). Each tracks observed changes of upward EP flux from the troposphere. Supported by changes of equatorial wind associated with the QBO, changes of EP flux account for much of the interannual variance of wintertime temperature and ozone (Hadjinicolaou et al. 1997, 2002, 2005; Salby and Callaghan 2002; Hu and Tung 2002)

TL;DR - looking at monthly correlations between QBO and 10mb wind, the strongest correlation for December is actually with previous June (0.45), January with previous September (0.43) and February with previous December (0.32). For winter 500mb 60°N zonal wind (or surface), there is no correlation. Wave driving is the major factor controlling the vortex ahead of QBO which affects how the wave driving behaves rather than direct momentum transfer, with vulcanicity, ENSO and solar very much in the background.

 

edit: forgot about dodgy values giving no proper QBO signal in the early years - why they bother including them is a mystery.

No matter, excluding the first 7 years so starting in 1955, takes the QBO > -20 years winter CET from 4.29 to 4.30.

Edited January 26, 2017 by Interitus

[Summer Sun]

 

[Ali1977]

44 minutes ago, Summer Sun said:

 

What is the forecast hPa are we at as we stand for this initail warming over the weekend, and earlier next week?  I'm guessing if we get wind reversal at or near 10hPa that's a big enough SSW to hopefully split the vortex, or atleast have a chance of doing so?

Edited January 26, 2017 by Ali1977

[Summer Sun]

39 minutes ago, Ali1977 said:

What is the forecast hPa are we at as we stand for this initail warming over the weekend, and earlier next week?  I'm guessing if we get wind reversal at or near 10hPa that's a big enough SSW to hopefully split the vortex, or atleast have a chance of doing so?

 

 

[Nick F]

6 hours ago, Ali1977 said:

What is the forecast hPa are we at as we stand for this initail warming over the weekend, and earlier next week?  I'm guessing if we get wind reversal at or near 10hPa that's a big enough SSW to hopefully split the vortex, or atleast have a chance of doing so?

Need a planetary wavenumber 2 to split the polar vortex, the current warming of the strat and displacement of the sPV is associated with wavenumber 1 activity. So in essence, need two planetary waves for the split. No signs of a sufficient wave 2 amplification to do this for now.

Edited January 26, 2017 by Nick F

[SMU]

The GFS MEAN forecast gets today the zonal wind down +2M/S & the ECM forecast is +3M/S

both @10 HPA

so no technical SSW..

Edited January 26, 2017 by Steve Murr

[Day 10]

Hannah Attard ‏@HannahAttard

As GFS and ECMWF back off in their u decel fcst NASA's GEOS-5 is full steam ahead. Associated with the near historical 10hPa heat flux fcst?

[bluearmy]

why would we take much notice of the nasa model in the strat. it hardly covers itself with any glory lower down ?

[Day 10]

10 minutes ago, bluearmy said:

why would we take much notice of the nasa model in the strat. it hardly covers itself with any glory lower down ?

I was simply passing on some info retweeted from Matt Hugo's twitter which some in here may find useful!

[bluearmy]

44 minutes ago, Day 10 said:

I was simply passing on some info retweeted from Matt Hugo's twitter which some in here may find useful!

Don't misunderstand me - I was more querying the value of the tweet from Hannah, not the post itself 

 

[mountain shadow]

1 hour ago, bluearmy said:

why would we take much notice of the nasa model in the strat. it hardly covers itself with any glory lower down ?

I suppose 10hpa is the edge of space so maybe thats the NASA models one strong point?

We will know soon enough.

[bluearmy]

Ec day 10 shows a much stronger second wave of warming at 10hpa than GFS op 

[Gray-Wolf]

J. Cohen has this to say about the upcoming/ongoing Strat event and his expected impacts;

https://www.aer.com/science-research/climate-weather/arctic-oscillation

of the impacts over Europe he says;

"Finally my thinking for why Europe could turn colder longer term is because of the possibility of the stratospheric PV being displaced towards Europe.  In my opinion this scenario increases in likelihood if there are multiple WAFz/poleward heat transport pulses.  If the stratospheric PV is displaced bodily into western Eurasia this would likely setup easterly flow across Northern Europe in the stratosphere followed by potentially the same in the troposphere.  But even if the stratospheric PV is not displaced into Europe but close to Europe, the flow around the PV across Europe will turn northerly in the stratosphere and could eventually turn northerly in the troposphere across Europe as well.  Either a northerly or easterly flow across Europe would transport colder air into the region.  This scenario is not predicted as the short-term response to the SSW/weak PV event but could be a lagged response starting sometime in February."

[Summer Sun]