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A melting Arctic and weird weather: the plot thickens

Posted on 20 February 2015 by Guest Author

By Jennifer Francis, Rutgers University

Everyone loves to talk about the weather, and this winter Mother Nature has served up a feast to chew on. Few parts of the US have been spared her wrath.

Severe drought and abnormally warm conditions continue in the west, with the first-ever rain-free January in San Francisco; bitter cold hangs tough over the upper Midwest and Northeast; and New England is being buried by a seemingly endless string of snowy nor’easters.

Yes, droughts, cold and snowstorms have happened before, but the persistence of this pattern over North America is starting to raise eyebrows. Is climate change at work here?

Wavier jet stream

One thing we do know is that the polar jet stream – a fast river of wind up where jets fly that circumnavigates the northern hemisphere – has been doing some odd things in recent years.

Rather than circling in a relatively straight path, the jet stream has meandered more in north-south waves. In the west, it’s been bulging northward, arguably since December 2013 – a pattern dubbed the “Ridiculously Resilient Ridge” by meteorologists. In the east, we’ve seen its southern-dipping counterpart, which I call the “Terribly Tenacious Trough.” (See picture, below.)

These long-lived shifts from the polar jet stream’s typical pattern have been responsible for some wicked weather this winter, with cold Arctic winds blasting everywhere from the Windy City to the Big Apple for weeks at a time.

We know that climate change is increasing the odds of extreme weather such as heatwaves, droughts and unusually heavy precipitation events, but is it making these sticky jet-stream patterns more likely, too? Maybe.

Slowing, drunken path

The jet stream is a dastardly complex creature, and figuring out what makes it tick has challenged atmospheric scientists since it was discovered about 75 years ago. Even more elusive is figuring out how climate change will affect it.

Jet streams exist because of differences in air temperature. In the case of the polar jet stream, which is responsible for most of the weather we experience around the middle-latitudes of the northern hemisphere, it’s the cold Arctic butting against warmer areas to the south that drives it. (A more in-depth explanation can be found here.) Anything that affects that temperature difference will affect the jet stream.

This is where climate change comes in: the Arctic is warming much faster than elsewhere. That Arctic/mid-latitude temperature difference, consequently, is getting smaller. And the smaller differential in temperatures is causing the west-to-east winds in the jet to weaken.

Strong jets tend to blow straight west to east; weaker jets tend to wander more in a drunken north/south path, increasing the likelihood of wavy patterns like the one we’ve seen almost non-stop since last winter.

When the jet stream’s waves grow larger, they tend to move eastward more slowly, which means the weather they generate also moves more slowly, creating more persistent weather patterns.

NASA/Goddard Space Flight Center Scientific Visualization Studio

At least, that’s the theory. Proving it is not easy because other changes are happening in the climate system simultaneously. Some are natural fluctuations, such as El Niño, and others are related to increasing greenhouse gases.

We do know, however, that the Arctic is changing in a wholesale way and at a pace that makes even Arctic scientists queasy. Take sea ice, for example. In only 30 years, its volume has declined by about 60%, which is causing ripple effects throughout the ocean, atmosphere, and ecosystem, both within the Arctic and beyond. I’ve been studying the Arctic atmosphere and sea ice my entire career and I never imagined I’d see the region change so much and so fast.

‘Stuck’ weather patterns

To study the effects of Arctic change on weather patterns, we have good measurements of atmospheric temperatures and winds going back to the late 1970s, when satellites started providing data, and pretty good measurements back to the late 1940s.

My colleagues and I have been using this information to measure the waviness of the jet stream and whether it is behaving differently since the Arctic started its rapid warm-up about 20 years ago. Because the upper atmosphere is such a cacophony of swirling winds, however, measuring changes in the jet stream’s waviness is tricky, as it’s not a metric that scientists have traditionally used.

Our challenge, then, is to find new methods to measure waviness and determine whether any changes we find are related to rapid Arctic warming, to some other change in the climate system, or to just random chance. While the story is still in early days, the plot is thickening.

Several groups around the globe, including my colleagues and me, are trying to understand the linkages between rapid Arctic warming and changes in weather patterns.

A number of recent studies have found what appears to be a solid connection between sea-ice loss in an area north of western Russia during the fall and a rash of abnormally cold winters in central Asia. The loss of sea ice favors a northward bulge in the jet stream, which strengthens surface high pressure to the east. That shift pumps cold Arctic air southward into central Asia.

Other studies suggest that Arctic warming in summer leads to a split jet stream – or two separated rivers of wind – which tends to trap the waves. Those stationary waves cause weather conditions to remain “stuck” for long periods, increasing the likelihood of extreme heat waves, droughts and flooding events in Eurasia and North America.

Our own new work, published last month in Environmental Research Letters, uses a variety of new metrics to show that the jet stream is becoming wavier and that rapid Arctic warming is playing a role. If these results are confirmed, then we’ll see our weather patterns become more persistent.

In other words, Ridiculously Resilient Ridges and Terribly Tenacious Troughs may become the norm, along with the weather woes they cause.

This article was originally published on The Conversation. Read the original article.

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Comments 1 to 9:

  1. In your research do you exclude the effects of Planetary-scale wave activity for stratospheric sudden warming events (SSW) that weaken the stratospheric Vortex (SVW)? It would seem that the primary driver for (troposphere) Northern Hemisphere Wintertime Weather is the propagation of the Arctic Oscillation from the stratosphere by SSW and SVW or I am confusing the issue in my head?

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  2. With the last SSW around the first of this January.

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  3. Living in California, I know the area has paleo (lake sediment) proxies showing extreme prolonged dry spells; one academic page has cites: —

    quoting from one:

    "Laird PNAS 2003 paper is a story about large-scale moisture shifts across the northern prairies of North America during the past 2000 years. Authors using 6 lake sediments across the North American prairies show that two different types of major shifts in moisture regimes (from wet to dry or from dry to wet) existed for at least the last two millennia.... Such large-scale moisture shifts were thought to be caused by the expansion of the polar vortex, and may be a common phenomenon which may reoccur over longer time frames. The differences in timing of moisture shifts were explained as the fluctuations in the position and shape of the jet stream."

    (They don't say _why_ the jet stream varied in the past, and I'm assuming you'd have to look through a lot of proxies over a large area to guess) 

    Is there enough data on year to year variability over the long term past to say what's happening now is within that "noise" or is a detectable climate signal emerging from the noise?

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    Moderator Response:

    [JH] Link activated.

  4. Another good discussion of these interconnections at robertscribbler: Mangled Jet Stream + Global Warming + Hot Atlantic Water = Boston Buried Under 8 Feet of Snow

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  5. RE Hank # 3, the Laird paper is cited by Cook et al in "Megadroughts in North America: placing IPCC projections of hydroclimatic change in along-term palaeoclimate context" ( 

    Global warming will expand the worlds dry lands polewards and make them drier: the IPCC AR4 Report said so and it makes sense.

    The Cook paper is mostly about model projections. It didn't say anything about a connection between past Mega droughts and the Jet Stream. Not surprising considering how little we understand the Jet Stream.

    It did say that the past megadroughts were connected to changes in solar activity (see this quote from the Conclusions: "There is no question now that profound megadroughts have occurred in North America during the last millennium, principally during MCA times and into the early part of the Little Ice Age. These droughts have occurred without any need
    for enhanced radiative forcing due to anthropogenic greenhouse
    gas forcing. There are additional model-based results suggesting that the MCA megadroughts were associated with enhanced warming during a time of increased solar irradiance."" Nothing was said about the changes affecting the Jet Stream?   

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  6. arctic-outbreak-shatters-records-in-eastern-u-s-coldest-yet-to-come/

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  7. In surprising news, there was another huge calving of the Jakobshavn glacier in West Greenland, of "Chasing Ice" fame, earlier this week:

    Shock News – Massive Calving of Jakobshavn Isbræ

    Although this is no longer the case today, the recent storms in the North Atlantic reduced Arctic sea ice extent to an all time record low for the date earlier this week:

    Shock News – IJIS Arctic Sea Ice Extent Lowest Ever!

    Is there a feedback loop here? Less sea ice => more open water => bigger storms => more wind and waves => less sea ice?

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  8. Another consequence of Arctic melt?

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  9. Yet more Arctic melting! A whole range of Arctic sea ice metrics are currently at their lowest ever levels for the date:

    Arctic Sea Ice Area Lowest Ever (For the Date!)

    What's more yet another storm is brewing!

    and air temperatures above the North Pole are much the same as on the shores of the Great Lakes.

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    Moderator Response:

    [RH] Resized image. Please keep images down to 500px so they don't break page formatting. Thx.

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