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Stratosphere and Polar Vortex Watch


Paul

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Posted
  • Location: Camborne
  • Location: Camborne

To improve seasonal storm track forecasts, look to the tropical stratosphere

Quote

People have become familiar with “bomb cyclones” this winter, as several powerful winter storms brought strong winds and heavy precipitation to the U.S. east coast, knocking out power and causing flooding. With strength that can rival that of hurricanes, bomb cyclones get their name from a process called bombogenesis, which describes the rapid intensification they undergo within 24 hours as they move along the coast.

These winter storms tend to form and travel within narrow “atmospheric conveyor belts”, called storm tracks, which can change location over a period of years.

Scientists have extensively studied potential causes behind these year-to-year changes in attempt to better forecast storm tracks and their extreme impacts, but new research from scientists at the Stony Brook University (SBU) School of Marine and Atmospheric Sciences, funded by NOAA Research’s MAPP Program, identifies another crucial controlling force.

After analyzing 38 years of model data, the research team found that an alternating pattern of winds high up in the tropical stratosphere, called the Quasi-Biennial Oscillation (QBO), affects significant year-to-year changes in both the North Pacific and North Atlantic storm tracks.

https://research.noaa.gov/News/NewsArchive/LatestNews/TabId/684/ArtMID/1768/ArticleID/13338/To-improve-seasonal-storm-track-forecasts-look-to-the-tropical-stratosphere.aspx

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For some time the GEFS have been predicting the summer wind reversal at the end of the runs for around 13th-15th April -

epsmean10hPa60N18040512.thumb.png.ef53b0985aaa72d8b7a2033f2da051f7.png

but the GFS has only recently consistently come into agreement about a week away -

umedel6018040512.thumb.png.5eaf5a92a93db4fbc78fda03ff04a4da.png

The GEOS from the 4th however still has weak westerlies (~3 m/s) for the 13th. As posted previously, not a 'final warming' but gradual dissipation with the increasing insolation, as expected.

Meanwhile, an interesting paper with regards to the effects of mountains has just been published, Orography and the Boreal Winter Stratosphere: The Importance of the Mongolian Mountains -

Quote

Abstract
The impact of mountains on stratospheric circulation is explored using the Whole Atmosphere Community Climate Model. The “Mongolian mountains” decrease the boreal winter stratospheric jet strength by ∼1/3 and increase the frequency of major sudden stratospheric warmings from 0.08 year−1 to the observed 0.60 year−1. These changes are twice the magnitude of the impacts of the Tibetan plateau and Himalayas. Consistent with the decrease in the zonal jet, there is enhanced Eliassen‐Palm flux convergence; this is predominantly from changes in wave propagation pathways through changes to the upper troposphere circulation, not from an increased amplitude of planetary waves reaching the stratosphere. The Mongolian mountains have the greater impact on upper tropospheric circulation due to their meridional location. The Rocky Mountains have no significant impact on the stratospheric jet. Changes in wave propagation in response to the Mongolian mountains are similar to those associated with major sudden stratospheric warming events in observations.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2018GL077098 - new so paywalled at the moment, but a pre-submission version is available here -

https://atmos.washington.edu/~david/White_etal_GRL_submitted2.pdf

 

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Posted
  • Location: Camborne
  • Location: Camborne
5 hours ago, lassie23 said:

How would this affect our weather, warm easterly?

Well I'm no expert on this but it could be we lose the quite intense Canadian vortex (transfer to N. Russia) and jet leaving N. America and the general pattern retrogresses with the European ridge taking closer order as it currently being indicated by the models. Which would be good news for the UK.

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  • 2 weeks later...
Posted
  • Location: Eastbourne and Larnaca,Cyprus .
  • Location: Eastbourne and Larnaca,Cyprus .

Thanks to all who contributed to this thread over the winter months .

Certainly that SSW delivered for coldies , let’s hope we get another next winter but a bit earlier in the season .

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  • 4 weeks later...
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Posted
  • Location: Netherlands
  • Location: Netherlands

This study uses reanalysis datasets and numerical experiments to investigate the influence of the occurrence frequency of the individual phases of the Madden–Julian oscillation (MJO) on the interannual variability of stratospheric wave activity in the middle and high latitudes of the Northern Hemisphere during boreal winter [November–February (NDJF)]. Our analysis reveals that the occurrence frequency of MJO phase 4 in winter is significantly positively correlated with the interannual variability of the Eliassen–Palm (E–P) flux divergence anomalies in the northern extratropical stratosphere; that is, higher (lower) occurrence frequency of MJO phase 4 corresponds to weaker (stronger) upward wave fluxes and increased (decreased) E–P flux divergence anomalies in the middle and upper stratosphere at mid-to-high latitudes, which implies depressed (enhanced) wave activity accompanied by a stronger (weaker) polar vortex in that region. The convection anomalies over the Maritime Continent related to MJO phase 4 excite a Rossby wave train that propagates poleward to middle and high latitudes, and is in antiphase with the climatological stationary waves of wavenumber 1 at middle and high latitudes. As the spatial distribution of the convection anomalies during MJO phase 7 has an almost opposite, but weaker, pattern to that during MJO phase 4, the occurrence frequency of MJO phase 7 has an opposite and weaker effect on the northern extratropical stratosphere to MJO phase 4. However, the other MJO phases (1, 2, 3, 5, 6, and 8) cannot significantly influence the northern extratropical stratosphere because the wave responses in these phases are neither totally in nor out of phase with the background stationary wavenumber 1.

https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-17-0476.1

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Posted
  • Location: New Forest (Western)
  • Weather Preferences: Fascinated by extreme weather. Despise drizzle.
  • Location: New Forest (Western)

That's a nice chunk of support for the existing theory tied in with GLAAM and the GWO, a very nice find Sebastiaan 

For those with very little time to spare - essentially (super-simplification alert), MJO phase 4 takes a + - + - wave pattern and adds it to the climatological - + - + pattern (opposites meet, waves suppressed), while MJO phase 7 adds - + - + to - + - + with exciting results.

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6 hours ago, Singularity said:

That's a nice chunk of support for the existing theory tied in with GLAAM and the GWO, a very nice find Sebastiaan 

For those with very little time to spare - essentially (super-simplification alert), MJO phase 4 takes a + - + - wave pattern and adds it to the climatological - + - + pattern (opposites meet, waves suppressed), while MJO phase 7 adds - + - + to - + - + with exciting results.

Too many +s and -s, they state stationary wavenumber 1 background state in the high latitudes.

Not sure why GLAAM and GWO gets dragged into this.

Edited by Interitus
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  • 4 weeks later...
Posted
  • Location: Near King's Lynn 13.68m ASL
  • Weather Preferences: Hoar Frost, Snow, Misty Autumn mornings
  • Location: Near King's Lynn 13.68m ASL
42 minutes ago, sebastiaan1973 said:

QBO june -28,45!

Eyeballing the record (since 1948), I can only see Feb 2015 as lower? Quite large error bars in these things though, I suppose, and there's the question of how homogeneous the whole record is for comparison.

Anyway, it seems to be following the classic phase pattern now through all the hPa levels unlike the anomaly of 2016.

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13 hours ago, Yarmy said:

Eyeballing the record (since 1948), I can only see Feb 2015 as lower? Quite large error bars in these things though, I suppose, and there's the question of how homogeneous the whole record is for comparison.

Anyway, it seems to be following the classic phase pattern now through all the hPa levels unlike the anomaly of 2016.

The first few years of the NCEP data from 1948 are particularly ropey.

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Posted
  • Location: Netherlands
  • Location: Netherlands

https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/asl.721

We present a case study of long range forecasts for Northern Hemisphere winter 2015/2016. This winter produced the strongest El Niño event since 1997/1998 and equatorial Pacific sea surface temperature anomalies exceeded 3 °C. Other factors relevant to the Northern Hemisphere extratropical atmosphere circulation included a strong westerly phase of the Quasi‐Biennial Oscillation (QBO) and very strong winds in the stratospheric polar night jet in early winter. At the surface, intense cyclonic extratropical circulation anomalies occurred in early winter in both the North Pacific and North Atlantic, consistent with known teleconnections to these phases of El Niño–Southern Oscillation, the QBO and the polar night jet. The midlatitude flow was very westerly in early winter and less westerly and sometimes northerly in late winter, when sudden stratospheric warming events also occurred. We show that initialised climate predictions were able to capture the winter mean flow pattern at seasonal lead times from well before the start of winter. In this special case, not only the winter mean flow pattern, but also some aspects of the sub‐seasonal evolution were skilfully predicted. We show that the winter of 1982/1983 was closely analogous to winter 2015/2016 in both the predictable driving factors and the forecast winter circulation. This case study adds to the evidence that the north Atlantic circulation can be predictable on seasonal timescales and advance warning of the increased risk of intense rainfall and storminess which caused extreme flooding in the UK in December was possible in this case.

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  • 3 weeks later...
Posted
  • Location: Camborne
  • Location: Camborne

Extratropical atmospheric predictability from the Quasi‐Biennial Oscillation in subseasonal forecast models

Quote

Abstract

The effect of the Quasi‐Biennial Oscillation (QBO) on the Northern Hemisphere wintertime stratospheric polar vortex is evaluated in five operational subseasonal forecasting models. Of these five models, the three with the best stratospheric resolution all indicate a weakened vortex during the easterly phase 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 Summary

The Quasi‐Biennial Oscillation (QBO) is perhaps the most regular atmospheric phenomena that isn't directly controlled by solar radiation, and can be predicted more than a 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 Hemisphere wintertime stratospheric polar vortex, and perhaps even the extratropical tropospheric circulation.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD028724#.W18oKaB-frE.twitter

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Posted
  • Location: Brighton (currently)
  • Location: Brighton (currently)

Is it certain that the QBO will be positive by winter? When is it expected to switch to the positive phase?

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Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
23 hours ago, karyo said:

Is it certain that the QBO will be positive by winter? When is it expected to switch to the positive phase?

Nobody quite knows but it should be near a peak now since the standardized value for July was -1.95 (most negative since Jan 15). 

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Posted
  • Location: Netherlands
  • Location: Netherlands

-29,10 for July. Well Karyo, it all depends how quickly it returns. Right now it's strongly negative but predicted to rise in the coming 10 days. Not all QBO-phases are the same, please see the graphic over here 

(thanks to Paul).

https://www.vwkweb.nl/index.php?page=Forum&articleid=138&reference=ref261795&threadpage=10

 

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On 03/08/2018 at 10:08, sebastiaan1973 said:

-29,10 for July. Well Karyo, it all depends how quickly it returns. Right now it's strongly negative but predicted to rise in the coming 10 days. Not all QBO-phases are the same, please see the graphic over here 

(thanks to Paul).

https://www.vwkweb.nl/index.php?page=Forum&articleid=138&reference=ref261795&threadpage=10

 

The lowest QBO on record in 70 years..

Can it recover from -29 to a positive in 5 months - remember though the impacts can be as early as Oct on the vortex -

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Posted
  • Location: Lincolnshire - 15m asl
  • Weather Preferences: Frost and snow. A quiet autumn day is also good.
  • Location: Lincolnshire - 15m asl
22 hours ago, Steve Murr said:

The lowest QBO on record in 70 years..

Can it recover from -29 to a positive in 5 months - remember though the impacts can be as early as Oct on the vortex -

I reckon not. Positive by the end of winter, but not Oct-Dec....though that is largely a guess

Edited by Catacol
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