Stratosphere and Polar Vortex Watch 2020

[Griff]

3 minutes ago, Griff said:

 

I know @Don and @bluearmy will have they're thoughts! 

 

2 minutes ago, Mike Poole said:

Stratobserve charts for todays GFS 0z run ridiculous:

Not sure what caused that.  Assuming that is a one off, strat vortex remains strong.  ECM T240 from Berlin:

I know others think otherwise but I favour a strong vortex now while it is not coupled to the trop.  One reason, that will make it less likely to couple sooner and to give the current trop patterns, which are interesting, to play out.  Second, if a SSW is going to do anything for us this year, it would be as a split, and I think that is more likely when the strat vortex is obliterated from a strong not weak base.  My bet SSW 15/1/22.  

Yes, I've just posted Denis' latest PV tweet...  

[Catacol]

56 minutes ago, Mike Poole said:

You make it sound so easy!  But as I have said before it is putting all our chips on a SSW for jam tomorrow when there may be other options closer to now.  I know you have said that cold is very unlikely these days without a SSW, so, effectively why bother!,  but I think the early part of this winter will test that.  Although the Greenland heights suggested by the models a week or so are watered down (it was never modelled a true Greenland high anyway), there is equally nothing to suggest a return to zonal.  A return to zonal after about 10 months now.  So I want to see that one out first, before chasing a SSW because I don’t think the trop precursors are there at the moment.  

Agreed Mike - no return to zonal in the next fortnight and a zonal pattern has been conspicuous by its absence throughout the autumn. Good for cold pooling perhaps especially if it were to continue throughout December - but the danger with that approach is that we get some nice frost and fog and signs of real winter, but meanwhile up top the lack of any vertical wave flux allows the upper vortex to override that helpful eQBO signal and couple with the troposphere. That is then a difficult hook up to prise apart unless tropospheric wave breaking hits the absolute sweet spot.

In the end there are many roads that can lead to cold, but perhaps some that are more likely to lead to jackpot cold than others. Right now we are cool for the foreseeable as all background signals are rather muted and therefore no obvious route to proper cold. It’s a bit too early in any case. But plenty of justified optimism in the longer term.

[Mike Poole]

17 minutes ago, Catacol said:

Agreed Mike - no return to zonal in the next fortnight and a zonal pattern has been conspicuous by its absence throughout the autumn. Good for cold pooling perhaps especially if it were to continue throughout December - but the danger with that approach is that we get some nice frost and fog and signs of real winter, but meanwhile up top the lack of any vertical wave flux allows the upper vortex to override that helpful eQBO signal and couple with the troposphere. That is then a difficult hook up to prise apart unless tropospheric wave breaking hits the absolute sweet spot.

In the end there are many roads that can lead to cold, but perhaps some that are more likely to lead to jackpot cold than others. Right now we are cool for the foreseeable as all background signals are rather muted and therefore no obvious route to proper cold. It’s a bit too early in any case. But plenty of justified optimism in the longer term.

It is like a game of poker, except the weather will do what it will whatever cards you have! There have been so many winters recently (all since 2011 really) when the only chance of a proper cold spell with snow for lowland areas has been as a result of a SSW.  I don’t think this is one of them,  and would like to see what the current dead Atlantic, amplified spell can do, before betting my last chips on a SSW.  

But hey, we’ve no control over any of it, it will be what it will be.  Hope it’s chips!  (Reminds me of an advert from yonks ago!).

Edited November 21, 2021 by Mike Poole

[Griff]

Perhaps heading towards the gfs... Slowly, slowly? 

If not, I'd still accept the middle ground for now. 

On 21/11/2021 at 19:15, Griff said:

 

Yes, I've just posted Denis' latest PV tweet...  

 

On 21/11/2021 at 20:05, Catacol said:

Agreed Mike - no return to zonal in the next fortnight and a zonal pattern has been conspicuous by its absence throughout the autumn. Good for cold pooling perhaps especially if it were to continue throughout December - but the danger with that approach is that we get some nice frost and fog and signs of real winter, but meanwhile up top the lack of any vertical wave flux allows the upper vortex to override that helpful eQBO signal and couple with the troposphere. That is then a difficult hook up to prise apart unless tropospheric wave breaking hits the absolute sweet spot.

In the end there are many roads that can lead to cold, but perhaps some that are more likely to lead to jackpot cold than others. Right now we are cool for the foreseeable as all background signals are rather muted and therefore no obvious route to proper cold. It’s a bit too early in any case. But plenty of justified optimism in the longer term.

 

23 hours ago, Mike Poole said:

It is like a game of poker, except the weather will do what it will whatever cards you have! There have been so many winters recently (all since 2011 really) when the only chance of a proper cold spell with snow for lowland areas has been as a result of a SSW.  I don’t think this is one of them,  and would like to see what the current dead Atlantic, amplified spell can do, before betting my last chips on a SSW.  

But hey, we’ve no control over any of it, it will be what it will be.  Hope it’s chips!  (Reminds me of an advert from yonks ago!).

 

[bluearmy]

Ec46 shows a decent n American high anomoly week 3 - in line with the gfs ops.

no sign of a raging vortex through December then  

[sheikhy]

1 minute ago, bluearmy said:

Ec46 shows a decent n American high anomoly week 3 - in line with the gfs ops.

no sign of a raging vortex through December then  

You got there before mattwolves!!!now thats something!!!!anyway good update mate!!!

[bluearmy]

1 minute ago, sheikhy said:

You got there before mattwolves!!!now thats something!!!!anyway good update mate!!!

He’s about as quick as coady! 

Frustratingly, ecm’s website offers a 10hpa eps chart but the data is never available beyond T12 

[Mike Poole]

NAM chart looking much more positive in the later forecast region re keeping the strat and trop vortexes separate, it was getting pretty close on previous runs - this from GFS 0z run :

[DavidS]

GFS 00z develops a decent warming at 10 hpa. It is days 14-16 so could disappear on the next run, but if it models this for a couple of days it will pique my interest.

 

[bluearmy]

1 hour ago, DavidS said:

GFS 00z develops a decent warming at 10 hpa. It is days 14-16 so could disappear on the next run, but if it models this for a couple of days it will pique my interest.

 

This is not a new signal 

the gefs have this warming and high anom centred over n America by 10th dec 

The ec46 also on that page 

 

[northwestsnow]

28 minutes ago, bluearmy said:

This is not a new signal 

the gefs have this warming and high anom centred over n America by 10th dec 

The ec46 also on that page 

 

Blue , I hate to second guess you but is it just CC and myself getting twitchy for Dec ?

[bluearmy]

3 hours ago, northwestsnow said:

Blue , I hate to second guess you but is it just CC and myself getting twitchy for Dec ?

Aaron is always twitchy 

I’m not twitchy but then again, I’m not confident in anything for December !  Mid lat ridge it is then! 

[mountain shadow]

Let's hope the Strat and Trop PV don't couple as the temps are now below average.

[northwestsnow]

1 hour ago, mountain shadow said:

Let's hope the Strat and Trop PV don't couple as the temps are now below average.

I think this has been forecast for a while..I was kinda hoping the eQBO would help  put the breaks on the vortex this Winter..

[mountain shadow]

31 minutes ago, northwestsnow said:

I think this has been forecast for a while..I was kinda hoping the eQBO would help  put the breaks on the vortex this Winter..

I think that is what is stopping a rampant trop PV, but it takes a lot more than an eQBO to deliver proper cold.

[fromey]

Anybody on here with far more experience than me care to explain these, these are emerging in twitter land.

[Interitus]

On 11/11/2021 at 20:55, Eagle Eye said:

We follow the warm air back to Asia

Direct quote

"There are a few clues that one can use to trace the origin of the descending warm air over the pole, but before looking at that, let's talk about that descending air in general. Of course the rapid descent of air in the stratosphere compresses and warms, but a key clue comes from knowing that it was already anomalously warm before it began to be compressed. What warmed it and where?

Thanks to satellite reanalysis data, we can in fact see exactly where the warm air came from before reaching the polar latitudes. As this animation so excellently displays, a wave of warm air moved up from
South Central Asia in the weeks prior to the SSW event that occurred in early January 2013. This wave in fact seems to almost "explode" up into the stratosphere, almost like the warming you'd get from a volcanic eruption (again, hence the reason for early theories on SSW's looking for a volcanic connection)."

Continuing with the analysis



This warm bubble rises due to the thermal wave that's over central Asia around the 21st December, the fact that this rises up so quickly indicates a very strong dynamical event which forced warm air up into the stratosphere from the troposphere.  It then moves northeast at 10 hPa stratospheric levels and higher. Here's different view of the thermal wave on December 28, 2013:

Here's another perspective on this wave that shows both its origin at lower latitudes, as well as it's progress toward the north. Remember, that this is occurring at the 10 hPa mid-stratosphere level:

This is a typical 'standard fingerprint' of an SSW, here's another one from an SSW in 2002 - 2003

Similar development in the thermal waves when it was developing at lower latitudes that year as well, there are similar waves before any SSW events as far as I know no example of it beginning in anywhere other than Asia, for example January 2009

 

When considering the development of these thermal waves at mid-stratospheric levels over Asia, there are several factors that must be considered. First, such of a rapid build-up of rising warm air can obviously not come from evaporation as normal adiabatic cooling would occur and we would see the exact opposite condition such as we find associated with the normal convective processes in thunderstorms or on a much larger scale in Hadley Cells.

Secondly, the consideration is that the rapidity necessary to bring such a large mass of warm air upward into the stratosphere. Some process must essentially "launch" this warm air up to the stratosphere, as we see it seems to "explode" into the stratosphere. The air has to be relatively warm to begin with (anomalously warm relatively to normal stratospheric temperatures at 10 hPa), for no matter how rapidly it is launched or how warm it was, it will expand and cool by some amount, no matter what. So in our search for the source of the thermal wave, we are looking for a source of warm air and a mechanism by which that air is launched rapidly upward into the stratosphere.

This is why some researchers suggested that volcanoes may be to blame for these waves though there isn't much evidence to support that.
 

Then we look for a High Positive Omega

The vertical rising or falling of air in the atmosphere is known as omega and is measured in Pascals per second (Pascal/s). A high positive omega over a geographic region would indicate that a significantly large mass of air was rapidly moving upward in that region, and likewise, a negative omega would indicate that a mass of air that was falling or moving downwards. 

In the formation of a thermal wave in the stratosphere over South Central Asia we would be looking for a region in the troposphere within the same rough region with an unusually high positive omega. It would have to be an area that displayed what would be much like vertical jet stream or plume of warm air moving rapidly upward in the troposphere, then through the tropopause, to form the thermal wave in the stratosphere.

"In looking at the omega reanalysis data for the period around the formation of the thermal wave that formed over Asia in December 2012, we find the following very interesting data that displays the average omega across the entire troposphere from 1000 hPa up to 100 hPa. This chart was further constrained to show the region of interest, namely South Central Asia from 60E to 110E longitude and 0 to 70N latitude: "

When looking at this reanalysis chart we see three regions of high positive omega. These regions represent areas where air was moving rapidly upwards across the troposphere averaged over the entire month. For the sake of simplicity, I chose to narrow my analysis down to the area which has the highest positive omega of the three, which was the one furthest north and west.  Here's a closer view of the omega in that region during December 2012:

Again, for a clearer understanding of omega when looking at the preceding diagram, you could imagine a stream of air moving right out of the centre of the red  area, outward from the model area. This stream would be flowing up through the entire depth of the troposphere during the month of December 2012. For the sake of comparison, here's the omega for the exact same region during the month of July 2012:

When we begin comparing the two, we see that the high omega over this region in December 2012 truly is at least a monthly anomaly and not a year-round feature of this region. So we at least now have a potential area for a vertical stream of air moving into the stratosphere to form the thermal wave in December 2012. 

Skipping a bit here as this is beginning to get quite long explaining an SSW in clear effect

Direct quote
 

"SSW's are marked by rapidly descending air over the polar region.  This air warms as it descends but we've seen that it was warmer than normal to begin with. Through reanalysis, we have seen that the air travelled to the high latitudes as a stratospheric thermal wave at 10 hPa. In looking at the origins of this thermal wave we find high omega areas just south of the Taklamakan Desert in the Kunlun Shan and Altun Mountains. When prevailing north to south winter winds blowing across the Taklamakan desert (and including possible energy from jet stream winds) are directed toward the Tibetan Plateau under the right conditions, the perfect topological lifting conditions occur, allowing the warmer air from the desert to ascend rapidly into the stratosphere where it builds into a thermal planetary wave of warmer air that is carried north by prevailing upper level winds.

Upon reaching the higher latitudes of the Arctic, the warmer air begins to descend rapidly, warming even more but also carrying enough momentum during the descent to drag mesospheric air down into the stratosphere as well. This intrusion of mesospheric air during SSW events has been well documented, but is outside the scope of my research. Suffice to say it has been measured by many researchers and can be identified through its unique chemical signature. One excellent recent source for more information on this is Kvissel et al., 2012. As illustrated earlier, the rapidly descending air in the stratosphere over the Arctic has effects or teleconnections that reach some 9,000 km away to the equator. Here we see that the momentum of the polar descending air pulls the air in the stratosphere up at the equator, such that this air cools and expands and creates a temporary temperature and pressure anomaly.

Again, here's another example of this from the large SSW event that occurred around January 21, 2009 where, in this equatorial stratosphere profile of temperature, you can readily see the effect of air being drawn upward into the stratosphere: "

 

Other Causal Elements of SSW's: The Winter Tropopause

I have only briefly mentioned the tropopause so far but it shouldn't be taken out of any discussion of the full dynamics of SSW's. The intrusion of rapidly ascending warm air into the stratosphere from the troposphere means that this stream must penetrate through the tropopause as it ascends.

There are also some topological circumstances with location of the Taklamakan desert next to the Tibetan Plateau. The desert provides the ideal source of warm air to be "launched" upward and the rapid and steep mountain Kunlun Shan and Altun Mountains are the perfect launch pad for this 'launch' as it were. With the winter winds prevailing from the desert toward the mountains in this region, it only takes the right set of circumstances to initiate the precursor events to an SSW. 

"We must however add the additional factors of the lower winter tropospheric height and the fact that the Kunlun Shan and Altun Mountains are at an ideal position for penetrating the tropopause with warm air from below as the tropopause drops down rapidly between 30 and 40 degrees, as seen in this simple illustration (B. Geerts and E. Linacre, 1997):"

 

Not only does the tropopause lower in the winter, it also drops down dramatically just at the point where the Kunlun Shan and Altun Mountains ranges are located and therefore this is ready to provide the necessary launch platform for warm air from the Taklamakan desert. It is quite possible that had these mountain ranges been located four to five hundred hundred kilometres further south where the tropopause is higher, that the character of NH SSW's and NH winters might be completely different, that is why such small things can have such massive changes across an entire Hemisphere's Winter for quite a few years.

 

"Investigating numerous SSW events using reanalysis data has shown that in every event that I could find reliable data on, the initial locus of the warm air has come from South Central Asia. I investigated one potential source of this warm air among several-- namely at the point where the Taklamakan Desert meets the Tibetan Plateau in the Kunlun Shan and Altun Mountain ranges. 

This combination provides an ideal topographically forced "launching pad" for warm air to be lifted up through the lowered winter tropopause into the stratosphere. This air is then advected as a thermal wave toward the northern latitudes where it eventually descends, warms further, and creates an SSW event. This diagram illustrates the overall dynamics of this entire process:

 

In addition to the extensive reanalysis data, there appears to be tangential corroborating evidence in support of this overall dynamic, such as the high level of dust in Greenland ice cores that has an origin point in the Taklamakan desert and Tarim Basin. This dust could be part of the thermal wave that descends over the Arctic during the SSW and is eventually deposited in Greenland ice.

Future research could focus on gathering mid-stratosphere air samples at 10 hPa during one of the thermal wave episodes, just prior to the SSW event. A high level of dust inside that thermal wave that could be identified through isotopic analysis as coming from the Taklamakan Desert and Tarim Basin would be strong evidence of the origin of the warm air. Other avenues of research should include the analysis of other regions of South Central Asia that also show high positive omega values in the days leading up to the formation of the 10 hPa thermal wave. It is quite possible that several high positive omega areas could be involved simultaneously or each during different SSW events. 

Finally, a close analysis of the regions involved in high positive omega events should be conducted to see what meteorological conditions exist to create the wind field energy necessary for topographic lifting. In addition to pressure zones and prevailing winds, energy from the lowering of the tropopause and the jet stream during winter could be an important source of energy for high positive omega events and the precursors to SSW's."

A lot of this has been direct quote's because I feel it better to quote than try changing it and explaining it further as it was already efficiently explained

This "theory" first did the rounds a few years ago and unfortunately it is as wrong now as it was then.

To start with, the Taklamakan desert and Tamir basin are not a source of warm air in winter, it is typically bitterly cold with temperatures below freezing.

For sake of argument and assuming anomalous warmth, a bigger issue is that positive omega represents sinking air - negative omega is rising air.

But the biggest problem is that it fails to grasp the stratification and stability of the atmosphere. Ironically it is dismissive of moist processes which actually go a long way to overcome the stability, but also the tropopause which magnifies the scale of the problem, and also that adiabatic cooling would continue up to 10mb.

A convenient way to examine it is with consideration of potential temperature to compare the density of air at different altitudes. Theoretically, parcels of air with equal potential temperature are equally buoyant and interchangeable. Indeed for much of the atmosphere this holds true with isolines of potential temperature forming natural flow pathways - see isentropic analysis.

At the 10mb level in the stratosphere, potential temperature might be in excess of 850K - this would be the temperature an air parcel here would have if brought down to 1000mb. Conversely, an air parcel from near the surface would have to be much more than anomalously warm to remain buoyant at 10mb, rather hundreds of degrees C.

Studies of large forest fires have shown estimated surface temperature perturbations of 60C initiating large pyro-cumulonimbus clouds but the significance of latent heat release from adiabatic processes was 3 times that of the sensible heating (ie the fire). This is able to overshoot into the lower strat like regular storms but further uplift is capped by the tropopause. Examination of volcanic eruption plumes shows only the largest would be capable of reaching above the middle stratosphere. In any circumstance it must also be remembered that air parcels in reality are subject to substantial mixing and entrainment of the ambient air.

So there is no 'launch pad' producing a plume of warm air to 10mb (even the driest desert air would produce clouds as evidence), mountain uplift creates air parcels which rapidly become denser than the environment and negatively buoyant, returning to their initial level - or actually oscillating above and below this level ie orographic gravity waves.

[bluearmy]

5 hours ago, fromey said:

Anybody on here with far more experience than me care to explain these, these are emerging in twitter land.

Warming over n America in two weeks - well signposted and pushes the spv back towards Asia 

[TSNWK]

On 25/11/2021 at 15:51, bluearmy said:

Warming over n America in two weeks - well signposted and pushes the spv back towards Asia 

Reduced risk of coupleing over Greenland... Although I guess we still have be concerned about an uncoupled trop vortex over Greenland... 

What would be nice by own simple logic is coupled vortex over Asia?

[fromey]

5 minutes ago, bluearmy said:

Warming over n America in two weeks - well signposted and pushes the spv back towards Asia 

Thanks @bluearmy, will be keeping an eye them then.

[Eagle Eye]

On 25/11/2021 at 14:44, Interitus said:

This "theory" first did the rounds a few years ago and unfortunately it is as wrong now as it was then.

To start with, the Taklamakan desert and Tamir basin are not a source of warm air in winter, it is typically bitterly cold with temperatures below freezing.

For sake of argument and assuming anomalous warmth, a bigger issue is that positive omega represents sinking air - negative omega is rising air.

But the biggest problem is that it fails to grasp the stratification and stability of the atmosphere. Ironically it is dismissive of moist processes which actually go a long way to overcome the stability, but also the tropopause which magnifies the scale of the problem, and also that adiabatic cooling would continue up to 10mb.

A convenient way to examine it is with consideration of potential temperature to compare the density of air at different altitudes. Theoretically, parcels of air with equal potential temperature are equally buoyant and interchangeable. Indeed for much of the atmosphere this holds true with isolines of potential temperature forming natural flow pathways - see isentropic analysis.

At the 10mb level in the stratosphere, potential temperature might be in excess of 850K - this would be the temperature an air parcel here would have if brought down to 1000mb. Conversely, an air parcel from near the surface would have to be much more than anomalously warm to remain buoyant at 10mb, rather hundreds of degrees C.

Studies of large forest fires have shown estimated surface temperature perturbations of 60C initiating large pyro-cumulonimbus clouds but the significance of latent heat release from adiabatic processes was 3 times that of the sensible heating (ie the fire). This is able to overshoot into the lower strat like regular storms but further uplift is capped by the tropopause. Examination of volcanic eruption plumes shows only the largest would be capable of reaching above the middle stratosphere. In any circumstance it must also be remembered that air parcels in reality are subject to substantial mixing and entrainment of the ambient air.

So there is no 'launch pad' producing a plume of warm air to 10mb (even the driest desert air would produce clouds as evidence), mountain uplift creates air parcels which rapidly become denser than the environment and negatively buoyant, returning to their initial level - or actually oscillating above and below this level ie orographic gravity waves.

Ah, to be fair I shouldn't have trusted just a couple articles on that my fault, the rest of it is definitely more trustworthy though

[Griff]

Ecm zonal latest, not raging, just fairly average. 

[Typhoon John]

On 25/11/2021 at 15:56, TSNWK said:

Reduced risk of coupleing over Greenland... Although I guess we still have be concerned about an uncoupled trop vortex over Greenland... 

What would be nice by own simple logic is coupled vortex over Asia?

When did we last have a coupled vortex over Asia?

[bluearmy]

Last few gfs ops have shown a stretching spv over the other side of the pole ……needs watching as it could lead to a split ……..more likely won’t but could have a ticket in the raffle ……

[summer blizzard]

Out of interest, do we know if 1975 had a SSW/attempted SSW in Jan or Feb.