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Stratosphere and Polar Vortex Watch


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4 hours ago, Blessed Weather said:

There's been some very interesting research lately into the impact of a warming climate on the future frequency of SSW's. Here are two such papers.

"No robust evidence of future changes in major stratospheric sudden warmings: a multi-model assessment from CCMI"

This August 2018 paper looks at the results from the 12 models involved in the 'Chemistry-Climate Model Initiative' and concludes:

  • No statistically significant changes in the frequency of occurrence of SSWs are to be expected in the coming decades and until the end of the 21st century. This result is robust, as it is obtained with three different identification criteria.
  • Other features of SSWs – such as their duration, deceleration of the polar night jet, and the tropospheric precursor wave fluxes – do not change in the future either in the model simulations, in agreement with other studies, such as McLandress and Shepherd (2009) and Bell et al. (2010).
  • The absence of a future change in SSWs is a robust result across all models examined here, regardless of their biases or different representation of the QBO, coupling to the ocean, solar variability, etc.

https://www.atmos-chem-phys.net/18/11277/2018/acp-18-11277-2018.pdf

On the other hand, this July 2017 paper finds there will be an impact:

"More Frequent Sudden Stratospheric Warming Events due to Enhanced MJO Forcing Expected in a Warmer Climate."

  • Given that the MJO is predicted to be stronger in a warmer climate, these results suggest that SSW events may become more frequent, with possible implications on tropospheric high-latitude weather.

https://www.seas.harvard.edu/climate/eli/reprints/Kang-Tziperman-2017.pdf

Note the first paper references the second and whilst accepting that it may be correct, it cautions against projecting upon one potential factor without taking into account changes in others which may counteract it.

Indeed this can be seen in the Kang-Tziperman follow-up papers which are perhaps more interesting, investigating further the mechanisms involved and also the longitudinal origin of the forcing which can reduce SSW as well as increase -

The Role of Zonal Asymmetry in the Enhancement and Suppression of Sudden Stratospheric Warming Variability by the Madden-Julian Oscillation - https://www.seas.harvard.edu/climate/eli/reprints/Kang-Tziperman-2018.pdf

and

The MJO-SSW Teleconnection: Interaction Between MJO-Forced Waves and the Midlatitude Jet https://www.seas.harvard.edu/climate/eli/reprints/Kang-Tziperman-2018b.pdf

 

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Some useful tropospheric developments upcoming which are likely to have stratospheric impacts towards the end of November and more particularly into December. A strong convectively coupled tropic

so after many days the GFS & FNMOC & canadian finally now follow the Euro with 44 out 64 Members with a split at day 9- The ECM is day 8. We will call it - SSW & Split for 1st Ja

For all that watch the zonal winds. Let me urge you to look at the geopotential heights more. At least as far as weakening/strengthening trends go. Because as the polar vortex cries for help, you migh

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6 hours ago, Interitus said:

Note the first paper references the second and whilst accepting that it may be correct, it cautions against projecting upon one potential factor without taking into account changes in others which may counteract it.

Indeed this can be seen in the Kang-Tziperman follow-up papers which are perhaps more interesting, investigating further the mechanisms involved and also the longitudinal origin of the forcing which can reduce SSW as well as increase -

The Role of Zonal Asymmetry in the Enhancement and Suppression of Sudden Stratospheric Warming Variability by the Madden-Julian Oscillation - https://www.seas.harvard.edu/climate/eli/reprints/Kang-Tziperman-2018.pdf

and

The MJO-SSW Teleconnection: Interaction Between MJO-Forced Waves and the Midlatitude Jet https://www.seas.harvard.edu/climate/eli/reprints/Kang-Tziperman-2018b.pdf

 

Another two interesting pieces of research that move our understanding forward, although the first paper maybe rather heavy on 'scientific theory' to test extreme scenarios and paper two acknowledging it ignores many important secondary factors that may negate their findings. I am left wondering whether (a) maybe the papers in my post are somewhat more realistic regarding medium term impact, and (b) much more work is needed before we can be certain about the likely future impact of climate warming in this area.

These statements, both from the conclusions of the respective papers, illustrate what I'm trying to say:

First Paper
"It should be noted that the analysis here is based on a highly idealized model, where the MJO is not explicitly simulated and moisture feedbacks are ignored, among other simplifications. While this allows a deeper under-standing of the results, a verification using more complete GCMs is required. We also note that, because of the relative low model top being used (3 mb), the SSW simulated in the idealized model may be not realistic. The strongest MJO forcing used here is 10 K day. This value is significantly larger than current values of 2–4 K day, but maybe possible in a 4 x CO2 or even more extreme warming scenarios. At a 10 K day forcing amplitude, the mean atmospheric state is significantly modified by the forcing. We discussed how these mean state changes affect the teleconnection mechanism, yet it is useful to keep in mind that the mean state is very different from the present-day atmosphere in this case, making it likely an unrealistic scenario, even if useful for understanding purposes."

Second Paper
"This work focused on the anticipated strengthening of the MJO in a warmer climate but did not take the expected change of the static stability, storm track, and other general circulation features into account. Such changes may affect the Arctic stratosphere directly and may also change the way the MJO impacts SSWs. Future work will need to consider not only changes to the MJO but also many other intervening factors that may change in response to a global warming (e.g., blocking events, stationary wave patterns, storm track structure, El Niño–Southern Oscillation, and Quasi-Biennial-Oscillation."

Edited by Blessed Weather
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8 hours ago, Steve Murr said:

@Blessed Weather

Its not stratospheric driven changes but climate change driving tropospheric induced decoupling !

Yes Steve. Maybe last season was a good example - the stratosphere and troposphere remained uncoupled through Autumn and it wasn't until late November that the two finally coupled, but interestingly it was the troposphere engaging and coupling with the lower/middle stratosphere, rather than the upper stratosphere driving its influence downwards.

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With a cooling stratosphere and warming troposphere, the potential instability is likely to reach record levels increasingly often.

One way to think about that is to take the old 'elastic band' analogy and envision that band being stretched out more rapidly and further, resulting in more dramatic snap-backs when the built-up potential is realised (the band is let go of). 

This translates as a stratospheric polar vortex that both ramps up and comes apart more quickly and dramatically than has been typical of preceding decades. Add in the fact that Arctic amplification really seems to mess with the vortex in ways that leave it more reliant on supportive stratospheric conditions to get going much in the first place, and the outlook for the coming decades is extremely interesting. Perhaps concerning, depending on your standing point.

 

I must caution, though, that a fair bit of the above is 'informed speculation' based on what I've observed over the past half-dozen years in particular. Sometimes, though, such exercises are needed, as the professional peer-review process often takes years to complete, by which time the actual situation has developed a whole lot further. Such is really messing with our ability to keep 'official' tabs on the way the Arctic, for example, is behaving these days.

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2 hours ago, Singularity said:

With a cooling stratosphere and warming troposphere, the potential instability is likely to reach record levels increasingly often.

One way to think about that is to take the old 'elastic band' analogy and envision that band being stretched out more rapidly and further, resulting in more dramatic snap-backs when the built-up potential is realised (the band is let go of). 

This translates as a stratospheric polar vortex that both ramps up and comes apart more quickly and dramatically than has been typical of preceding decades. Add in the fact that Arctic amplification really seems to mess with the vortex in ways that leave it more reliant on supportive stratospheric conditions to get going much in the first place, and the outlook for the coming decades is extremely interesting. Perhaps concerning, depending on your standing point.

 

I must caution, though, that a fair bit of the above is 'informed speculation' based on what I've observed over the past half-dozen years in particular. Sometimes, though, such exercises are needed, as the professional peer-review process often takes years to complete, by which time the actual situation has developed a whole lot further. Such is really messing with our ability to keep 'official' tabs on the way the Arctic, for example, is behaving these days.

Not quite sure what you're getting at - with regards to instability the strongly increasing equivalent potential temperature (theta-e) with height portrays stability of the stratosphere - look at a few radiosonde soundings of the stratosphere (eg. here http://weather.uwyo.edu/upperair/sounding.html) and you will see the change in trop/strat temperatures required is far in excess of any change so far.

What changes in the relative trop/strat temperatures does is alter the tropopause height.

 

Edited by Interitus
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Ah yes I see my mistake there @Interitus; potential instability is its own scientific measure... I meant it less literally i.e. how potentially unstable i.e. rapidly fluctuating the system may become, as the stratospheric vortex may intensify more rapidly in a colder stratosphere, but then come under stronger attack from the warmer troposphere (greater energy available for the wave packets that lead to vertical wave propagation), within which the polar vortex may be less stable as well in the sense that it struggles to come together or stay in one piece for very long.

Hopefully that makes more sense... if not, I may try again when more sober ?.

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On 11/08/2018 at 12:34, Steve Murr said:

Whilst some of us begin to break out of early hibernation-

I noted todays 3 CFS runs for very late autumn indicating very weak stratospheric winds

6D988530-C768-4EE3-95CB-B602F04254B7.thumb.png.c447658d050900097d3cce98ce04046f.png

I tried to add some more members from recent cfs runs (all members from last week) and its quite clear that according to cfs  the vortex will get a tough start of the season. Interesting to see such an impressive signal and will be interesting to see how it verifies. 

1651112017_laddaned(1).thumb.png.3324bd34721f2fa9bc1a79b021730d28.png

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8 hours ago, Mattias said:

I tried to add some more members from recent cfs runs (all members from last week) and its quite clear that according to cfs  the vortex will get a tough start of the season. Interesting to see such an impressive signal and will be interesting to see how it verifies. 

1651112017_laddaned(1).thumb.png.3324bd34721f2fa9bc1a79b021730d28.png

Sorry to be slightly off topic but where did you get this from by any chance (or the ensemble data)? It would be very appreciative, thanks.

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12 hours ago, BruenSryan said:

Sorry to be slightly off topic but where did you get this from by any chance (or the ensemble data)? It would be very appreciative, thanks.

The ensemble data is from CFS, downoloaded from here: http://nomads.ncep.noaa.gov
I did the chart by myself so at the moment it is only on our server, but hopefully it will soon be possible to interactively add more ensemble data to the chart at  http://weatheriscool.com/index.php/stratosfaren-zonalvind-10hpa-60n-gfs-ens/

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37 minutes ago, Mattias said:

The ensemble data is from CFS, downoloaded from here: http://nomads.ncep.noaa.gov
I did the chart by myself so at the moment it is only on our server, but hopefully it will soon be possible to interactively add more ensemble data to the chart at  http://weatheriscool.com/index.php/stratosfaren-zonalvind-10hpa-60n-gfs-ens/

Thanks, Mattias. Are you aware of any bias in the CFS regarding the Strat vortex strength? I ask because @Recretos has shown that the GEFS underestimate the vortex strength.

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2 hours ago, Yarmy said:

Thanks, Mattias. Are you aware of any bias in the CFS regarding the Strat vortex strength? I ask because @Recretos has shown that the GEFS underestimate the vortex strength.

That's a very good question. I do not have that much experience of the cfs, but it is of course a bit suspicious when more or less all the members behaves like they do in the chart above. I also found this link(http://www.nws.noaa.gov/ost/climate/STIP/FY11CTBSeminars/jperlwitz_092210.htm) where they confirms that there is (or at least used to be) a bias towards weaker polar vortex states in the CFS so the data should be used with great caution. In this case I think it would have been nice to use some kind of model climate (instead of "real" climate) for comparison to get a more realistic signal. 

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https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018JD028724 

Abstract
The effect of the Quasi-Biennial Oscillation (QBO) on the Northern Hemisphere wintertimestratospheric polar vortex is evaluated in five operational subseasonal forecasting models. Of these fivemodels, the three with the best stratospheric resolution all indicate a weakened vortex during the easterlyphase of the QBO relative to its westerly phase, consistent with the Holton-Tan effect. The magnitude of this effect is well captured for initializations in late October and November in the model with the largest ensemble size. While the QBO appears to modulate the extratropical tropospheric circulation in some of the models as well, the importance of a polar stratospheric pathway, through the Holton-Tan effect, for the tropospheric anomalies is unclear. Overall, knowledge of the QBO can contribute to enhanced predictability,at least in a probabilistic sense, of the Northern Hemisphere winter climate on subseasonal timescales.
Plain Language SummaryThe Quasi-Biennial Oscillation (QBO) is perhaps the most regularatmospheric phenomena that is not directly controlled by solar radiation and can be predicted more thana year in advance. It is characterized by alternating westerly and easterly winds in the tropical stratosphere.Here we show that the QBO can be used to improve month-ahead prediction of the Northern Hemispherewintertime stratospheric polar vortex, and perhaps even the extratropical tropospheric circulation.

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19 hours ago, Steve Murr said:

Today is day 1 of 2018 Winter vortex.!!! 

Positive 0.1M/S - An early start for the PV.

Im quite excited this winter as the prospect of something very tasty coming along-

Sea ice anomalies in the 2 key regions very significant in terms of worse than usual & the CFS modelling of the stratosphere showing that as we start to hit the colder months through Autumn so the strat may run much lower than usual..

Still about 6 weeks to go before we see the reality - but early excitement builds..

 

Great work @Mattias

Todays CFS runs see a SSW mid November - similar to 1962..

Why is the polar vortex forming a food think?

I read this  https://www.metoffice.gov.uk/learning/atmosphere/polar-vortex

And I'm just a little confused. Surely it is better for the polar vortex to not form so cold air can come down?

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13 minutes ago, snowy weather said:

Why is the polar vortex forming a food think?

I read this  https://www.metoffice.gov.uk/learning/atmosphere/polar-vortex

And I'm just a little confused. Surely it is better for the polar vortex to not form so cold air can come down?

Its just the 'classification' of the vortex

when the 10mb winds go positive - thats the date the PV has formed-

It wont have a bearing on winter just yet as we need to see how the strength builds through October - Nov-

The weak sun should impact it in terms of making it weaker-

Also over the last decade - areas of low heights over the NH (50-70N) in Autumn have been notably absent-

ENSO signal will be very weak & QBO whilst decending Westerly should still be weak Easterly @50HPA through October ( currently around -22 ) so again a low impact weak vortex event...

So far so good in the world of the stratosphere...

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52 minutes ago, snowy weather said:

Why is the polar vortex forming a food think?

I read this  https://www.metoffice.gov.uk/learning/atmosphere/polar-vortex

And I'm just a little confused. Surely it is better for the polar vortex to not form so cold air can come down?

It always forms at this point of the year....it just depends where it ends up in the depths of winter that will allow the epic shots of cold to perhaps come our way, or if it is a strong westerly vortex then we will inevitably have our usual plate of wind rain and mildness.

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1 hour ago, Steve Murr said:

Its just the 'classification' of the vortex

when the 10mb winds go positive - thats the date the PV has formed-

It wont have a bearing on winter just yet as we need to see how the strength builds through October - Nov-

The weak sun should impact it in terms of making it weaker-

Also over the last decade - areas of low heights over the NH (50-70N) in Autumn have been notably absent-

ENSO signal will be very weak & QBO whilst decending Westerly should still be weak Easterly @50HPA through October ( currently around -22 ) so again a low impact weak vortex event...

So far so good in the world of the stratosphere...

Thanks for the explanation.

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1 hour ago, mb018538 said:

It always forms at this point of the year....it just depends where it ends up in the depths of winter that will allow the epic shots of cold to perhaps come our way, or if it is a strong westerly vortex then we will inevitably have our usual plate of wind rain and mildness.

OK thanks. 

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On 24/08/2018 at 09:39, knocker said:

 

Well, the mode vs the mean - the GEOS analysis gave westerlies returning on 24/08 which is exactly the average date for the mean zonal wind to become positive in the MERRA reanalysis

Date            Data   Minimum     10%     30%    Mean     70%     90% Maximum   Fcst
2018-08-23     -0.18     -2.70   -1.46   -0.72   -0.21   -0.01    0.23    0.55      0
2018-08-24      0.64     -2.91   -1.01   -0.32    0.12    0.30    0.71    1.58      0

https://ozonewatch.gsfc.nasa.gov/meteorology/figures/merra2/wind/u60n_10_2018_merra2.txt

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Morning

Once again the CFS models paint a clear picture for the stratosphere & continue to be very very interesting for the period November & December with a very subdued vortex & A late November Warming event... 

Not many November/December Warming years to choose from In the archives ( 1962 springs to mind )

E8CFEAB1-6FDF-4EEF-8A51-A9CED3794E57.thumb.png.ee5044c2453d25a26c892c678c4bd811.png

Edited by Steve Murr
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