Stratosphere Temperature Watch 2015/2016

[chris55]

That exert from the Cohen blog is interesting, a SSW sometime in Jan leading to some severe winter weather across NH is certainly a possibility by the sounds of it. In the mean time it would be nice if we could squeeze something more seasonable out of this pattern before the big one!

[MPG]

1 hour ago, chris55 said:

That exert from the Cohen blog is interesting, a SSW sometime in Jan leading to some severe winter weather across NH is certainly a possibility by the sounds of it. In the mean time it would be nice if we could squeeze something more seasonable out of this pattern before the big one!

Link please.

[MPG]

Just now, Greenland1080 said:

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

Thanks.

[MPG]

"We continue to anticipate that the polar vortex will be sufficiently perturbed/weakened to allow colder weather to spread over the Northern Hemisphere mid-latitudes starting in January.   Still, If the energy transfer is not sufficiently strong over the next month or so to weaken the polar vortex, then the winter AO is likely to average positive in the mean and a mild weather pattern will dominate the mid-latitude continents for the remainder of the winter."

No confidence from Cohen regarding next year.......IF we do we do, if we don't we don't. The more likely outcome will be the AO will stay around positive.

[Gael_Force]

He appeared to be more confident last year but it didn't work out; perhaps being a bit more restrained this year. To me it all looks too much like last year at this time: hopes pinned on a similar MJO phasing and waves that didn't have enough oomph.

[karyo]

10 minutes ago, Gael_Force said:

He appeared to be more confident last year but it didn't work out; perhaps being a bit more restrained this year. To me it all looks too much like last year at this time: hopes pinned on a similar MJO phasing and waves that didn't have enough oomph.

Agreed! I think hopes for January are slowly fading. 

If something happens it will be for February or March.

[Interitus]

Well with regards to last year it was actually a substantial warming setting some daily temperature records at some levels, though it appeared the wave forcing may have just tailed off too soon.

Looking at a couple of current analogues for this year shows how similar set ups can give different results but also the potential forecastability of the stratosphere. The two closest 30-day analogues to the GEOS 10mb 60°N wind forecast for 31/12/15 are 09/01/1981 and 12/01/2000 - this is as calculated by way of mean square difference over 30 days. This is shown in the graph below, dark blue = 2015, orange = 1981, yellow = 2000, cyan = analogue average.

Both analogues show a reduction in wind speed starting within the next couple of weeks, with 2000 almost achieving SSW - windspeed 0.6 m/s after 27 days - this shows the fairly typical amount of time required to get to a wind reversal from the current level, so eg 27th Jan 2016.

1981 didn't reverse till later in the season but what is remarkable firstly is the similarity in profile of the variation in wind speed between the two years, the correlation over the next 60 days is 0.857.

But why the difference in wind speed? Maybe the forcing was different, however then remarkably again, the 60°N 10mb wave 1 geopotential height for the two years was almost identical -

Remember, this match in wave 1 profile was not selected directly but by similarity of the previous 30 day wind speed to this year.

Ultimately 2015/6 might not follow either of these years, but analogues for the other variables tend to give similar results of possibly end of January or start of February though certainly not guaranteed.

Edited December 23, 2015 by Interitus

[chris55]

5 hours ago, MPG said:

"We continue to anticipate that the polar vortex will be sufficiently perturbed/weakened to allow colder weather to spread over the Northern Hemisphere mid-latitudes starting in January.   Still, If the energy transfer is not sufficiently strong over the next month or so to weaken the polar vortex, then the winter AO is likely to average positive in the mean and a mild weather pattern will dominate the mid-latitude continents for the remainder of the winter."

No confidence from Cohen regarding next year.......IF we do we do, if we don't we don't. The more likely outcome will be the AO will stay around positive.

The exert above is talking about a weakening of the PV, possibly weakening the vortex enough to allow something more seasonal at the front end of Jan. I was talking about the possible SSW, though as Cohen says this is by no means certain just something to watch out for, and if it doesn't happen in Jan then i fear this winter as a whole will be rather forgettable in terms of cold, though this record warm Dec is certainly not forgettable!

"Therefore, based on the polar vortex model and the upcoming atmospheric circulation pattern, we are anticipating more upward pulses of WAFz. If the predicted atmospheric circulation pattern is correct and our expectations of more upward pulses of WAFz is correct, this should be sufficient to force a sudden stratospheric warming (SSW) sometime in January. And if our expectations of a weakened polar vortex verify, this will likely favor an increased likelihood of severe winter weather across the continents of the Northern Hemisphere "

Edited December 23, 2015 by chris55

[BrickFielder]

 Stratosphere forecasting is probably just as complicated as traditional weather forecasting and when you break things down there are both positive and negative factors which will affect whether a stratospheric warming will occur. Before I get into these factors lets just recap a few basics about stratospheric warmings.

Warmings tend to come in three flavours. The first is a minor warming  (wave 1) which tends to push the stratospheric vortex away from the pole and tend to be common. These warmings can often push the vortex towards the UK resulting in wet and windy weather while setting up blocked weather patterns elsewhere. This blocked pattern can often provide the conditions for a major warming to follow in two to three weeks time. A major warming (wave 2) will tend to split the vortex in two and tends to be a little less common than minor warmings. The result for the UK depends on where the two lobes of the vortex are at a particular point, but often you can expect a slowly moving blocked pattern giving a cold spell for the UK. Finally there is the final warming which indicates the break up of the stratospheric vortex and ultimately the polar vortex which can lead to a variable pattern and some cold out breaks over the UK.

These warmings are caused by upward propagating planetary waves  (Rossby Waves). OK so let me explain what I think these planetary waves are and how they work. Wave 1 represents a blocking  pattern where there is a single major blocking high pressure in northern latitudes. Typically this blocking high is connected to the Siberian High or norther European high pressure in Winter. Wave 2 represents a blocking pattern where there are two major blocking high pressure areas in northern latitudes. Typically these might be North western Canada  and Siberia. Wave 3 would represent three blocking highs in northern latitudes. Placement of the blocking high also seems to play a key role with a suggestion that  Blocking Highs  over  the  Euro-Atlantic  sector  tend  to  enhance  the  upward propagation  of  Planetary waves,  whereas  blocking highs  over  the  western  Pacific  lead  to  a  strengthening  of  the  polar  vortex.

OK if you want to know more and see how these work follow the link below.

http://www.sparc-climate.org/fileadmin/customer/5_Meetings/GA5_PDF/KazuakiNishii_SPARC_GeneralAssembly2014_14Jan.pdf

So any old high pressure in winter will cause a stratospheric warming? No it is never quite that simple and there are precursor and conditions for these waves to propagate upwards into the stratosphere and affect the polar vortex. One source of precursors is possibly gravity waves in key areas with these smaller scale waves being able to penetrate above the stratosphere (mesosphere and ionosphere) to affect conditions there which will slow the winds slightly at the top levels of the stratosphere. These lowered winds then become susceptable to planetary waves disturbing them.

Another link which sort of skirts around this.

http://www.sparc-climate.org/fileadmin/customer/5_Meetings/GA5_PDF/PosterSessionB.pdf

Now your head is probably totally confused about different waves I have better give a brief explanation of what gravity waves are as opposed to planetary waves. Gravity waves tend to result from either thunderstorms or low pressure systems crossing over mountain ranges. It turns out that particular mountain ranges and storms systems tend to have a large effect on whether planetary waves affect the stratospheric vortex. These gravity wave hot spots in the northern hemisphere winter include the mountains of Norway, Greenland and the UK. This might suggest that wet and windy weather in the UK and Norway might be a precursor to a stratospheric warming.

Another link with some nice maps of where gravity wave hot spots occur.

http://onlinelibrary.wiley.com/doi/10.1029/2012JD018658/full

So we are starting to get a bit of a picture about how stratospheric warmings might come about. I have of course missed out on Kelvin Waves (particularly relevant to Tibetan plateau in winter) and solar tides. I am sure somebody here will go away and check up on these things to give an even clearer picture.

Link explaining how all the different wave types combine together.

http://arxiv.org/pdf/1412.0077.pdf

Waves are part of the story but there is perhaps one more dimension that needs exploring a little and this is around ozone amounts over the pole. Ozone concentrations over the pole at high levels in the stratosphere alter the temperatures at those levels. Ozone depletion at the top of the stratosphere results in warming at this level and cooling through lower layers in the stratosphere. When temperatures go below -78 C Polar Stratospheric Clouds form which deplete the ozone further. This causes increased wind speeds in the stratospheric vortex which become ever harder to displace  (i.e. No amount of planetary waves could shift it). One cause of ozone depletion in the top layer of the stratosphere is the pulling down of Nox from layers above due to Energetic Particles. What I think this means is that space weather or more particularly solar activity can play a part in whether   stratospheric warmings occur (Note that EPP activity while related to the solar cycle can be slightly different).  Gravity waves can off course play a part in excitation of the thermosphere and mesosphere changing ozone concentrations as well.

A little bit of discussion about this at the following link.

http://www.atmos-chem-phys-discuss.net/15/33283/2015/acpd-15-33283-2015.pdf

Seems to me that Geomagnetic activity might play a part as well.

http://www.swpc.noaa.gov/products/notifications-timeline

So having said all that and knowing a little about the drivers are we any closer to understanding whether a stratospheric warming is likely this winter ? The answer I think is that there are some   possibilities as energy is transferred from the troposphere into the stratosphere, but that we have a very strong stratospheric vortex which is going to take some shifting. After the current wave which we should not expect to shift the vortex much there is another wave forecast for around the 5th of January. I don't expect much from that one either but it might set up the conditions ready for a      further wave. So I think we are looking at late January and into February as realistic windows of      opportunity. Much will depend on ozone depletion due to cold stratospheric temperatures against ozone transport from lower latitudes.

[chris55]

Excellent post^^^

[Dennis]

3 hours ago, BrickFielder said:

 Stratosphere forecasting is probably just as complicated as traditional weather forecasting and when you break things down there are both positive and negative factors which will affect whether a stratospheric warming will occur. Before I get into these factors lets just recap a few basics about stratospheric warmings.

Warmings tend to come in three flavours. The first is a minor warming  (wave 1) which tends to push the stratospheric vortex away from the pole and tend to be common. These warmings can often push the vortex towards the UK resulting in wet and windy weather while setting up blocked weather patterns elsewhere. This blocked pattern can often provide the conditions for a major warming to follow in two to three weeks time. A major warming (wave 2) will tend to split the vortex in two and tends to be a little less common than minor warmings. The result for the UK depends on where the two lobes of the vortex are at a particular point, but often you can expect a slowly moving blocked pattern giving a cold spell for the UK. Finally there is the final warming which indicates the break up of the stratospheric vortex and ultimately the polar vortex which can lead to a variable pattern and some cold out breaks over the UK.

These warmings are caused by upward propagating planetary waves  (Rossby Waves). OK so let me explain what I think these planetary waves are and how they work. Wave 1 represents a blocking  pattern where there is a single major blocking high pressure in northern latitudes. Typically this blocking high is connected to the Siberian High or norther European high pressure in Winter. Wave 2 represents a blocking pattern where there are two major blocking high pressure areas in northern latitudes. Typically these might be North western Canada  and Siberia. Wave 3 would represent three blocking highs in northern latitudes. Placement of the blocking high also seems to play a key role with a suggestion that  Blocking Highs  over  the  Euro-Atlantic  sector  tend  to  enhance  the  upward propagation  of  Planetary waves,  whereas  blocking highs  over  the  western  Pacific  lead  to  a  strengthening  of  the  polar  vortex.

OK if you want to know more and see how these work follow the link below.

http://www.sparc-climate.org/fileadmin/customer/5_Meetings/GA5_PDF/KazuakiNishii_SPARC_GeneralAssembly2014_14Jan.pdf

So any old high pressure in winter will cause a stratospheric warming? No it is never quite that simple and there are precursor and conditions for these waves to propagate upwards into the stratosphere and affect the polar vortex. One source of precursors is possibly gravity waves in key areas with these smaller scale waves being able to penetrate above the stratosphere (mesosphere and ionosphere) to affect conditions there which will slow the winds slightly at the top levels of the stratosphere. These lowered winds then become susceptable to planetary waves disturbing them.

Another link which sort of skirts around this.

http://www.sparc-climate.org/fileadmin/customer/5_Meetings/GA5_PDF/PosterSessionB.pdf

Now your head is probably totally confused about different waves I have better give a brief explanation of what gravity waves are as opposed to planetary waves. Gravity waves tend to result from either thunderstorms or low pressure systems crossing over mountain ranges. It turns out that particular mountain ranges and storms systems tend to have a large effect on whether planetary waves affect the stratospheric vortex. These gravity wave hot spots in the northern hemisphere winter include the mountains of Norway, Greenland and the UK. This might suggest that wet and windy weather in the UK and Norway might be a precursor to a stratospheric warming.

Another link with some nice maps of where gravity wave hot spots occur.

http://onlinelibrary.wiley.com/doi/10.1029/2012JD018658/full

So we are starting to get a bit of a picture about how stratospheric warmings might come about. I have of course missed out on Kelvin Waves (particularly relevant to Tibetan plateau in winter) and solar tides. I am sure somebody here will go away and check up on these things to give an even clearer picture.

Link explaining how all the different wave types combine together.

http://arxiv.org/pdf/1412.0077.pdf

Waves are part of the story but there is perhaps one more dimension that needs exploring a little and this is around ozone amounts over the pole. Ozone concentrations over the pole at high levels in the stratosphere alter the temperatures at those levels. Ozone depletion at the top of the stratosphere results in warming at this level and cooling through lower layers in the stratosphere. When temperatures go below -78 C Polar Stratospheric Clouds form which deplete the ozone further. This causes increased wind speeds in the stratospheric vortex which become ever harder to displace  (i.e. No amount of planetary waves could shift it). One cause of ozone depletion in the top layer of the stratosphere is the pulling down of Nox from layers above due to Energetic Particles. What I think this means is that space weather or more particularly solar activity can play a part in whether   stratospheric warmings occur (Note that EPP activity while related to the solar cycle can be slightly different).  Gravity waves can off course play a part in excitation of the thermosphere and mesosphere changing ozone concentrations as well.

A little bit of discussion about this at the following link.

http://www.atmos-chem-phys-discuss.net/15/33283/2015/acpd-15-33283-2015.pdf

Seems to me that Geomagnetic activity might play a part as well.

http://www.swpc.noaa.gov/products/notifications-timeline

So having said all that and knowing a little about the drivers are we any closer to understanding whether a stratospheric warming is likely this winter ? The answer I think is that there are some   possibilities as energy is transferred from the troposphere into the stratosphere, but that we have a very strong stratospheric vortex which is going to take some shifting. After the current wave which we should not expect to shift the vortex much there is another wave forecast for around the 5th of January. I don't expect much from that one either but it might set up the conditions ready for a      further wave. So I think we are looking at late January and into February as realistic windows of      opportunity. Much will depend on ozone depletion due to cold stratospheric temperatures against ozone transport from lower latitudes.

Credits to AER - Pls use a link for the WAF plot : http://www.aer.com/science-research/climate-weather/arctic-oscillation

Edited December 23, 2015 by Dennis

[Dennis]

Hi what can any tell me about this 10Hpa sign  : 2 strong PV 's

[Interitus]

5 minutes ago, Dennis said:

Hi what can any tell me about this 10Hpa sign  : 2 strong PV 's

It isn't 2 strong PVs - look at the geopotential chart for the same time -

The temperatures don't always match the vortex position, especially after the initial early season cooling and the first disturbances and wave breaking affects the vortex.

[Singularity]

 

The chart on the left acts as a reasonable summary of the GFS output of late for the 7-16 day period; a huge blocking high over Asia with quite a deep trough over the UK. Good for wave breaking from Asia coupled with the mountain-forced gravity waves in the UK and Norway as BrickFielder has introduced me to the idea of.

There's also some attempt to build ridges through Canada which suggest that potential for a bit of wave 2 warming somewhere along the way.

The resulting warming on the 12z is shown on the right. It always seems to kick off in the final few frames of each run!

Edited December 23, 2015 by Singularity

[lorenzo]

Thank you Interitus for the u and wave plots, very neat symmetry there. Also great post Brickfielder, some solid reading within. The EPF area is something I am just finding material on now and is of interest wrt to impacts and also the oscillations within.

Following up on the wave descriptions-  the W 1-2-3 at a visual quick glance is offered via JMA. http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/

From the same page as these which you may have seen regularly over time.

This page also plots EP Flux components and looking good as the current transfer across 100hPa busiest of season.

From the first paper linked in Brickfielder's post - 100-hPa eddy heat flux ([V*T*]) is used as a measure of upward PW propogation into the stratosphere.

Eddy Heat Flux plots are found in greater detail here http://acdb-ext.gsfc.nasa.gov/Data_services/Current/seasonal_strat/seasonal_strat.html

Here is our current forecast, alongside this the 'what happens next' with respect to the zonal wind profile of the vortex...

 

[Nouska]

Excellent posts above.

The energetic particle aspect seems to be an interesting focus of a lot of the current solar research. There have been some multi-discipline papers presented this year but very difficult to find any free to view.

Although the current sun spot numbers are very similar to the last SSW in December 2012, the geomagnetic activity is much greater than then.

SSN

2012  current  

Edited December 24, 2015 by Nouska

[Recretos]

 Stratosphere forecasting is probably just as complicated as traditional weather forecasting and when you break things down there are both positive and negative factors which will affect whether a stratospheric warming will occur. Before I get into these factors lets just recap a few basics about stratospheric warmings.

Warmings tend to come in three flavours. The first is a minor warming  (wave 1) which tends to push the stratospheric vortex away from the pole and tend to be common. These warmings can often push the vortex towards the UK resulting in wet and windy weather while setting up blocked weather patterns elsewhere. This blocked pattern can often provide the conditions for a major warming to follow in two to three weeks time. A major warming (wave 2) will tend to split the vortex in two and tends to be a little less common than minor warmings. The result for the UK depends on where the two lobes of the vortex are at a particular point, but often you can expect a slowly moving blocked pattern giving a cold spell for the UK. Finally there is the final warming which indicates the break up of the stratospheric vortex and ultimately the polar vortex which can lead to a variable pattern and some cold out breaks over the UK.

These warmings are caused by upward propagating planetary waves  (Rossby Waves). OK so let me explain what I think these planetary waves are and how they work. Wave 1 represents a blocking  pattern where there is a single major blocking high pressure in northern latitudes. Typically this blocking high is connected to the Siberian High or norther European high pressure in Winter. Wave 2 represents a blocking pattern where there are two major blocking high pressure areas in northern latitudes. Typically these might be North western Canada  and Siberia. Wave 3 would represent three blocking highs in northern latitudes. Placement of the blocking high also seems to play a key role with a suggestion that  Blocking Highs  over  the  Euro-Atlantic  sector  tend  to  enhance  the  upward propagation  of  Planetary waves,  whereas  blocking highs  over  the  western  Pacific  lead  to  a  strengthening  of  the  polar  vortex.

A very good read altogether BrickFielder, but there are some points that confuse me. Mainly its the bold areas above. Minor, Major, Final warmings kinda classify separately, based on the amount of disturbance or damage done to the polar vortex and the state of its zonal angular momentum in a multilayer spectrum. What i am trying to say, is that you can have minor warmings via wave 2, or major warmings induced by wave 1. The wave number does not specify directly which warming will occur or if at all, but more the dynamics of the polar stratosphere, to put it smple.   winters 12/13 and 13/14 are good examples. 

And Final warming is kinda a seperate feature, which marks the point of no return for the polar vortex, or the warming after which the polar vortex does not reform or re-establish enough energy to revive the PNJ (polar night jet), until next autumn. Or in another words, the state of the polar stratosphere remains mainly zonally reversed. A final warming happens every year, if not with the help of an SSW, than it happens naturally as we head towards spring or into April, may, when the seasonal sun angle changes and the stratosphere seasonally warms, and establishes a polar anti-vortex throughout the summer. Final warming is not really a type of an SSW, but is a rather a sub-classification thing. An SSW is not a final warming, but a sudden stratospheric warming, which can also be a final warming, So basically its both if it happens, but in essence its still treated as an SSW which also happened to be a final warming, if it would happen, lets say in late February or early March, and so on, because its kinda rare to have an SSW worthy of a final warming in early January for example...

Regards

[BrickFielder]

   Thanks to Dennis for pointing out that I should have put the source for the WAF diagram. So just to reminds us.

Credits to AER  for the WAF plot : http://www.aer.com/science-research/climate-weather/arctic-oscillation

  I think that 10hpa plot from Dennis's post shows an elongated stratospheric vortex due to the transfer of energy from the troposphere. Think ECMWF plots are a little different.

http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html

  This elongated pattern I think should set up some opportunities for high pressure blocking in the near future which may set us up for a warming later.
Wave 3 Pattern possibly coming up.

Wave 2 Patern to follow.

Ideally they should be further north though.  Plots are from the winter diagnostics link mentioned above.

From the temperature plots in Lorenzo's post I notice the stratospheric temperatures are lower than normal at both 10hpa and 30hpa which makes me think of ozone destruction and possible intensification of the stratospheric vortex later. It also usually means that at 1hpa to 5hpa there may have been a warming.

In reply to recretos when he says

The wave number does not specify directly which warming will occur or if at all.   Yes I absolutely agree that the wave number does not determine the type of warming, but I think a major warming is more likely from a wave 2 or 3 than from a wave 1 disturbance.   Yes final warmings will happen without a troposphere disturbance but can at times be precipitated by instigated by a disturbance.

If I get anything slightly wrong or over simplify then remember I am still learning as well. So I welcome all clarifications.

 

[Interitus]

14 hours ago, Singularity said:

 

The chart on the left acts as a reasonable summary of the GFS output of late for the 7-16 day period; a huge blocking high over Asia with quite a deep trough over the UK. Good for wave breaking from Asia coupled with the mountain-forced gravity waves in the UK and Norway as BrickFielder has introduced me to the idea of.

There's also some attempt to build ridges through Canada which suggest that potential for a bit of wave 2 warming somewhere along the way.

The resulting warming on the 12z is shown on the right. It always seems to kick off in the final few frames of each run!

There are a couple of things to point out - in the first chart with the large high over Asia only the western portion north of the Caspian sea offers increased geopotential height to streamflow at higher levels, that over eastern Siberia is a surface high formed by dense cold air near the surface, this is typically all below 500mb - as can be seen the 500mb height is at a similar level to that over areas of low pressure but much warmer average temperature between the surface and 500mb.

This leads to the second image which hints at a common misconception, the warming is not wave breaking from Asia, it is a result of the vortex being perturbed by the stratospheric Aleutian high. This has its roots over the western Pacific towards north America and tilts westwards and polewards with height to the Aleutian area.

Over short timescales stratospheric flow is highly isentropic, it follows levels of constant potential temperature not constant pressure. Using a Lagrangian approach, with an unperturbed vortex the pressure and temperature are related and the air parcels at different pressure levels can be thought simply as spinning like a roundabout.

However when the pressure levels experience a differential forcing such as by the Aleutian high the potential temperature isentropes and geopotential height become misaligned and the air parcels rise and fall round the vortex - the roundabout has become a carousel.

The warming in the second chart is in an area where the flow is sinking and warming adiabatically and these areas can often be seen in charts of geopotential at different heights where instead of being vertical over the pole for example, the vortex centre is forced to different locations, typically westward with height. When the contours and flow at one level crosses troughing at lower levels the flow descends and warms, when it crosses a ridge it rises and cools.

[Recretos]

2 hours ago, BrickFielder said:

 The wave number does not specify directly which warming will occur or if at all.   Yes I absolutely agree that the wave number does not determine the type of warming, but I think a major warming is more likely from a wave 2 or 3 than from a wave 1 disturbance.   Yes final warmings will happen without a troposphere disturbance but can at times be precipitated by instigated by a disturbance.

If I get anything slightly wrong or over simplify then remember I am still learning as well. So I welcome all clarifications.

Well, yes I think that too partially, but thinking or believing should not bend the facts a bit, since someone who doesnt know this subject, might get confused when seeing a minor warming with wave 2 or major warming with wave 1. Its just to reduce possible confusion. Wave 1 is a wave 1¸ and wave 2 is wave 2. And minor SSW is minor, and major SSW is major. If there would only be minor SSWs from wave 1s, than I wouldn't say anything, and the same goes for wave 2. The fact is, that one must not link specific wave numbers to specific SSW types, because the stratosphere does not work that way.  We had wave 1 major SSW in 12/13 season, and strong wave 2 with no major or even minor SSW in 13/14 season.

And again, the final warming is just a secondary name, or kinda like a suffix to the SSW. You can have the final warming without an SSW, and you can have an SSW without the final warming. Its just something that is added to the event later, if the vortex fails to recuperate.

Dont get me wrong, I am learning too, as always, and I am just trying to explain a thing or two a bit further, so there wont be any confusion. I know what you meant, but someone who does not know this field very well, might find some things confusing or contradicting down the line. 

happy holidays,

Regards 

Edited December 24, 2015 by Recretos

[Gael_Force]

1 hour ago, Recretos said:

Dont get me wrong, I am learning too, as always, and I am just trying to explain a thing or two a bit further, so there wont be any confusion. I know what you meant, but someone who does not know this field very well, might find some things confusing or contradicting down the line. 

Good explanation and though you are right about confusion, the majority looking for cold will not give a fig out of their Xmas pudding, what number the waves are as long as it gets the job done.

Merry Christmas to you all!!

[Vorticity0123]

 

4 hours ago, BrickFielder said:

 This elongated pattern I think should set up some opportunities for high pressure blocking in the near future which may set us up for a warming later.
Wave 3 Pattern possibly coming up.

Wave 2 Patern to follow.

Ideally they should be further north though.  Plots are from the winter diagnostics link mentioned above.

Thanks for the great posts all, they really help to improve our understanding of stratospheric meteorology! Keep up the good work.

The plots shown above do raise a few questions for me though. Previously these plots left me completely confused, but now I think I am closer to understanding them. First, I'll start off with trying to explain them as far as I am able to myself.

Potential temperature, stability and potential vorticity

If I understand them correctly, the plots show the potential vorticity amounts at the 380K isentropic (read: iso-potential-temperature) surface. In the stratosphere, the potential temperature increases rapidly with height. The same applies for potential vorticity.

In the troposphere, potential vorticity levels generally stay rather low (around 1 PVU) mainly because the temperature profile is not very stable. Once the stratosphere is reached, the potential temperature increases rapidly with height. As a result, the potential vorticity increases rapidly with height as well (due to high static stability). The point (the height of the tropopause) where this happens depends on the pressure below this height. In general, troughing implies a low tropopause height whereas ridging indicates a relatively high height of the tropopause. There are two main reasons for that.

1. In the example of troughing, the tropopause is reached very quickly. This means that temperature profile becomes very stable at a low altitudes. (and thus that potential vorticity increases rapidly with height starting from a low altitude).
2. Troughing is always associated with high values of relative vorticity. This means that potential vorticity is high in areas of troughing as well.

Where is the stratospheric vortex?

For simplicity I assume that isentropic surfaces are roughly equivalent to height surfaces.

Potential vorticity at the 380 K surface as of 23-12 00Z, T+120. Source: FU Berlin.

Based on the information above and from previous posts, I have indicated where I would roughly expect the polar vortex (inside the black line, denoted by L) and ridges ("H") would be present in the stratosphere (assuming that the 380K surface is in the lower stratosphere). High values of potential vorticity correspond to low 'heights', and low values of potential vorticity to high 'heights' (also a high tropopause height and therefore ridging below).

As a check, let's see how well this pattern indicated above matches the height pattern at 100 hPa.

 

Heights at the 100 hPa level (lower stratosphere) as of 23-12 00Z, T+120. Source: FU Berlin.

There are quite some simliarities between the two analyzed plots. Ridging is present in both cases over Scandinavia, Siberia and Alaska. So from this point of view the reasoning presented above seems like a sound one at a first glance.

Questions

Still, there are a few questions which puzzle me up to now.

1. Does the above analysis make sense in the way presented below? Or am I thinking a wrong way?
2. In the potential vorticity image we can see there is a strong gradient of potential vorticity at some places (e.g. above the Atlantic Ocean). Do these areas indicate strong temperature/height differences between these areas, and thereby a strong westerly flow.

Thanks in advance for answering these questions, and of course best wishes for 2016!

 

Edited December 24, 2015 by Vorticity0123
Removed redundant image

[Singularity]

4 hours ago, Interitus said:

There are a couple of things to point out - in the first chart with the large high over Asia only the western portion north of the Caspian sea offers increased geopotential height to streamflow at higher levels, that over eastern Siberia is a surface high formed by dense cold air near the surface, this is typically all below 500mb - as can be seen the 500mb height is at a similar level to that over areas of low pressure but much warmer average temperature between the surface and 500mb.

This leads to the second image which hints at a common misconception, the warming is not wave breaking from Asia, it is a result of the vortex being perturbed by the stratospheric Aleutian high. This has its roots over the western Pacific towards north America and tilts westwards and polewards with height to the Aleutian area.

Over short timescales stratospheric flow is highly isentropic, it follows levels of constant potential temperature not constant pressure. Using a Lagrangian approach, with an unperturbed vortex the pressure and temperature are related and the air parcels at different pressure levels can be thought simply as spinning like a roundabout.

However when the pressure levels experience a differential forcing such as by the Aleutian high the potential temperature isentropes and geopotential height become misaligned and the air parcels rise and fall round the vortex - the roundabout has become a carousel.

The warming in the second chart is in an area where the flow is sinking and warming adiabatically and these areas can often be seen in charts of geopotential at different heights where instead of being vertical over the pole for example, the vortex centre is forced to different locations, typically westward with height. When the contours and flow at one level crosses troughing at lower levels the flow descends and warms, when it crosses a ridge it rises and cools.

Thanks for those pointers, the first one is something I've thought about a lot when it comes to highs materialising to our northeast that are of such nature. They can be resilient to getting pushed aside but lack much of an upper level component as you say.

Your second point is intriguing to me as I've been thinking that the wave breaking leads to the stratospheric ridge and hence the more dramatic warming. Is that right or is the ridge formation independent of that process?

Cheers and have a great Christmas 

[Singularity]

The more significant warming is edging a little closer in time, now kicking off within the next fortnight.

The consistency of the past dozen runs with respect to this event occurring is encouraging.

[Dennis]

A great sign in the strato??