What is causing the extreme cold over North America?

The weather over North America has been hitting the headlines over the last few days with record breaking cold conditions spreading south from the Arctic. This has been linked to a ‘polar vortex’, but what is this and what could it mean for the UK?

What is the Polar Vortex?

The Polar Vortex is a term normally used to describe the persistent large-scale low pressure area situated around 50km above the poles in the stratosphere. When the vortex breaks down the eastern US is often cold, but this breakdown hasn’t happened yet. It is not clear to what extent the Polar Vortex is influencing surface weather at the moment.

What is happening over the USA?

The American use of the phrase ‘polar vortex’ referring to the extremely cold conditions over North America is slightly different to traditional definition above. It refers to features lower in the atmosphere – in the troposphere, where our weather happens.

In the winter a deep reservoir of cold air becomes established through the atmosphere over the Arctic because of the lack of sunlight. This is usually held over high latitudes by the jet stream.

What is happening over North America is that the jet stream has weakened and moved southwards in the wake of a low pressure system as it moved east over the Atlantic.  This allowed the reservoir of cold air to move southwards across the US, resulting in extremely low temperatures.

What does it mean for the UK? Does it mean it will get cold here?

Not at the moment. We get our coldest weather in the winter when the winds blow from the northeast or east – so from the continent.

In fact the cold weather in the US can strengthen the jet stream and bring the UK milder and wetter weather, much as we have seen over the last few days.

Currently our winds are blowing from the west and, while we will see the temperatures dropping from the mild conditions we have had during December, they will only be returning to something much closer to normal for the time of year.

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20 Responses to What is causing the extreme cold over North America?

  1. John Benton says:

    Straightforward factual information without even an oblique reference to climate change. Keep this going and the Met Office will regain credibility.

    • jbenton2013 says:

      Oh dear, I spoke too soon.

      I thought the Met Office had turned a corner but no soon had I said that than the Met Office chief climate alarmist gets his name splashed all over yesterdays newspapers claiming that the extreme weather of the last few days in Britain and the cold in the US are the cause of climate change.

      Running out of grant money Peter?

    • jbenton2013 says:

      Perhaps if Peter Stott is so sure the “extreme weather” of the last few days is being caused by climate change as he has claimed so often in interviews over the last few days he can write the next article on this blog setting out the data.

    • jsam says:

      Does the Met Office link the vortex to climate change – some of their staff seem to? Why the reticence?

      The Effect of Climate Change on the Variability of the Northern Hemisphere Stratospheric Polar Vortex

      Daniel M. Mitchell, Scott M. Osprey, and Lesley J. Gray
      National Centre for Atmospheric Science, University of Oxford, Oxford, United Kingdom

      Neal Butchart and Steven C. Hardiman
      Met Office Hadley Centre, Exeter, United Kingdom

      Andrew J. Charlton-Perez
      Department of Meteorology, Reading University, Reading, United Kingdom

      Peter Watson
      Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, United Kingdom

      With extreme variability of the Arctic polar vortex being a key link for stratosphere–troposphere influences, its evolution into the twenty-first century is important for projections of changing surface climate in response to greenhouse gases. Variability of the stratospheric vortex is examined using a state-of-the-art climate model and a suite of specifically developed vortex diagnostics. The model has a fully coupled ocean and a fully resolved stratosphere. Analysis of the standard stratospheric zonal mean wind diagnostic shows no significant increase over the twenty-first century in the number of major sudden stratospheric warmings (SSWs) from its historical value of 0.7 events per decade, although the monthly distribution of SSWs does vary, with events becoming more evenly dispersed throughout the winter. However, further analyses using geometric-based vortex diagnostics show that the vortex mean state becomes weaker, and the vortex centroid is climatologically more equatorward by up to 2.5°, especially during early winter. The results using these diagnostics not only characterize the vortex structure and evolution but also emphasize the need for vortex-centric diagnostics over zonally averaged measures. Finally, vortex variability is subdivided into wave-1 (displaced) and -2 (split) components, and it is implied that vortex displacement events increase in frequency under climate change, whereas little change is observed in splitting events.


      • jbenton2013 says:

        More model nonsense there Jsam. Nothing but “if'”, “could”, “may be”, “implied” etc etc. Science for arts graduates and true believers.

      • nuwurld says:

        Hi John. Thanks for the link. But hey, once there is a “glaring” error that the 7 authors and the peer reviewers and you, great digger of the proverbial, haven’t noticed in the abstract, well, you start to wonder.

        I can tell you have not made the error, but the scientists themselves as the abstract is word perfect. But still accountably incorrect.

        This excerpt is in disagreement with acknowledged facts.

        ” Analysis of the standard stratospheric zonal mean wind diagnostic shows no significant increase over the twenty-first century in the number of major sudden stratospheric warmings (SSWs) from its historical value of 0.7 events per decade, ”

        0.7 per decade, mmmmmh.

        Here is a list of some major SSW’s,

        FEB ’51
        FEB ’52
        JAN ’55
        JAN ’57
        JAN ’58
        JAN ’63
        FEB ’66
        JAN ’68
        JAN ’70
        JAN ’71
        JAN ’73
        JAN ’74
        JAN ’77

        13 in 26 years John.

        Does that sound like “0.7 per decade” of vortex splitting warmings?

        Recently we have had a major in Feb 2009 and another in Jan 2013. Or 2 within 5 years.

        Historically we have around 5 “majors” per decade, or 0.5 per year.

        Thanks for undermining an otherwise “little known” AGW paper whilst simultaneously displaying your own inability to keep up with a topic and showing your total reliance on “peer review” without understanding a word of what is said.

        Have a nice day.

      • jsam says:

        Good to see jbenton and nuwurld practicing their anti-science. 🙂

        I look forward to seeing Nu’s response published in AmetSoc. 🙂 (It won’t be because it’s nonsense.)

        As for Mr Benton and his anti-science obsession with absolutes… He could be wrong and should be told.

        —95% is the gold standard.

        They said gravity is a good example of something more certain than climate change. Climate change “is not as sure as if you drop a stone it will hit the Earth,” Princeton University climate scientist Michael Oppenheimer said. “It’s not certain, but it’s close.”

        Arizona State University physicist Lawrence Krauss said the 95 percent quoted for climate change is equivalent to the current certainty among physicists that the universe is 13.8 billion years old.
        The president of the prestigious National Academy of Sciences, Ralph Cicerone, and more than a dozen other scientists contacted by the AP said the 95 percent certainty regarding climate change is most similar to the confidence scientists have in the decades’ worth of evidence that cigarettes are deadly.

        “What is understood does not violate any mechanism that we understand about cancer,” while “statistics confirm what we know about cancer,” said Cicerone, an atmospheric scientist. Add to that a “very high consensus” among scientists about the harm of tobacco, and it sounds similar to the case for climate change, he said.


      • nuwurld says:

        Look John, just answer the question. What is the historical periodicity of major SSW’s?

        Is it 0.7 per decade, as you have quoted?

        With knowledge that the paper said the rate hasn’t changed and we have had two within five years, and the history I have seen shows ~5 per decade, just answer yes or no.

        Everybody demands accuracy from scientific statements.

      • nuwurld says:

        John, I totally disagree with your quoted “95% certainty”.

        Modern climate science has failed at the most basic level by ignoring the mass of evidence we have that shows that the climate is naturally variable.

        In order to ascertain the disruptive effects of any unnatural forcing a complete and accepted understanding of the natural drivers is required.

        This has never been achieved and therefore cannot be subtracted to reveal any anthropological factoring.

        We have wonderful data sets like those from the British Antarctic Survey where the ice core data reveals that the natural system can and has repeatedly produced changes of this magnitude.

        0.8degC is nothing unusual over 100 years. This warming has been numbered 343 of similar magnitude events. Some 46 have been identified as having a significantly higher rate of 1.2degC per century.

        People like you are the true deniers. You deny that the Earth/solar system is inherently variable. Your 95% confidence level undermines reason. It is utterly meaningless and unsupported by recent data. 17 years now with no statistically significant warming.

        100% of the people paid to study man’s effects upon the climate, realise that without such effects, they need another career!

        To reiterate,

        The 95% certainty of warming, that plainly isn’t happening, is delusional.

        Any attribution of recent climate change effects to warming, that hasn’t recently happened, is also therefore, delusional.

        That’s not science you speak of John, that’s blind “faith”.

      • jsam says:

        I look forward to nuwurld citing his reputable sources.

        But don’t hold your breath. Blue isn’t a becoming facial colour.

  2. gojam says:

    Reblogged this on theneedleblog and commented:
    Polar Vortex (uppercase) and ‘polar’ vortex (lowercase) explained and why the UK will soon be experiencing normal temperatures for the time of year over the next few weeks.

  3. nuwurld says:

    Dear Met. Some things I agree with here and some I don’t.

    The Americans have used the term “a polar vortex” to describe what has recently descended upon the US. However, I’m sure we both agree that, for the Arctic, there is only one polar vortex. It either exists, symmetrical about its axis of rotation, or it is in some form of disruption.

    Having monitored the polar vortex recently I have noticed a disturbance the likes of which I am sure you are aware. The vortex was stable up to around the 28th December 2013. A stratospheric instability occurring possibly slightly prior to this around the Himalayan plateau triggered a non advective propagation of thermal dissipation which ran up to the polar region. By the 31st of December 2013 the polar vortex was already subject to this stratospheric warming and by the 4th of January the now very compressed vortex had extended a lobe across North America. At this time a cold, dense region of cold air was already on its way to engulf most of the North American continent. Now I know correlation isn’t causation but you can see the area of doubt. Spatial and temporal alignment.

    You do say in this post,

    “This breakdown hasn’t happened yet”,

    which may have been slightly weighted at the time of writing as the breakdown was under way. Now, as I am writing the vortex is disturbed and is double poled and has swung back with some emphasis now towards the Asian continent.

    I do not believe this to be a major stratospheric warming. But it is a sudden stratospheric warming as it has disrupted the originally symmetrical vortex. It will be interesting to see if any insurgence of cold penetrates eastwards and disrupts the prevailing European westerlies as a result. I am sure you are monitoring this.

    I’m afraid that I cannot cut you any slack over this comment,

    ” a deep reservoir of cold air becomes established through the atmosphere over the Arctic because of the lack of sunlight. This is usually held over high latitudes by the jet stream.”

    The Jet stream does not contain the polar convective cell.

    The polar convective cell is density driven to replace the matter advected poleward at altitude. Relative energy and the pressure gradients depict how exactly the returning cold dense air meets the less dense, warmer air circulating thermal energy along the horizontal thermal gradient from equator to pole.

    As said before, the jet stream and mid latitude cold cored cyclones are a product of the thermal gradient at the confluence of the polar front and the warmer poleward extent of the Ferrel cell. The greater the temperature difference the more energetic the cyclones and the jet stream. But they are both products of and entirely dependent upon the existence and position of the polar front. Neither the cyclones nor the jet stream can re engineer the relative energies or densities of those convective cells. A simple relative energy estimation makes this fact.

  4. Yr blog wd be much improved if its entries were timed and dated. Also: yr comments on Cameron’s PMQ remarks are much in the media but nowhere on yr blog, so it’s hard to get yr actual view except as refracted thru’ more or less partisan reports. I’d welcome a response.

  5. jsam says:

    More extreme weather is costing us. Climate change is not free. The plaintiff does not succeed on any of its challenges to the three decisions of NIWA in issue. The application for judicial review is dismissed and judgment entered for the defendant. [and] The defendant is entitled to costs.

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