Jet stream changes since 1960s linked to more extreme weather, say researchers

Posted: January 12, 2018 by oldbrew in atmosphere, Natural Variation, research, weather

Wavy jet stream
[image credit: BBC]


The team say they have found ‘a strong driver of climate extremes in Europe for the last 300 years’, which obviously pre-dates the Industrial Revolution and its ’emissions’ by a wide margin.

Increased fluctuations in the path of the North Atlantic jet stream since the 1960s coincide with more extreme weather events in Europe such as heat waves, droughts, wildfires and flooding, reports a University of Arizona-led team.

The research is the first reconstruction of historical changes in the North Atlantic jet stream prior to the 20th century, reports Phys.org.

By studying tree rings from trees in the British Isles and the northeastern Mediterranean, the team teased out those regions’ late summer weather going back almost 300 years—to 1725.

“We find that the position of the North Atlantic Jet in summer has been a strong driver of climate extremes in Europe for the last 300 years,” Trouet said.

Having a 290-year record of the position of the jet stream let Trouet and her colleagues determine that swings between northern and southern positions of the jet became more frequent in the second half of the 20th century, she said.

“Since 1960 we get more years when the jet is in an extreme position”, Trouet said, adding that the increase is unprecedented.

When the North Atlantic Jet is in the extreme northern position, the British Isles and western Europe have a summer heat wave while southeastern Europe has heavy rains and flooding, she said.

When the jet is in the extreme southern position, the situation flips: Western Europe has heavy rains and flooding while southeastern Europe has extreme high temperatures, drought and wildfires.

“Heat waves, droughts and floods affect people,” Trouet said. “The heat waves and drought that are related to such jet stream extremes happen on top of already increasing temperatures and global warming—it’s a double whammy.”

Extreme summer weather events in the American Midwest are also associated with extreme northward or southward movements of the jet stream, the authors write.
“We studied the summer position of the North Atlantic jet. What we’re experiencing now in North America is part of the same jet stream system,” Trouet said.

This winter’s extreme cold and snow in the North American Northeast and extreme warmth and dryness in California and the American Southwest are related to the winter position of the North Pacific Jet, she said.

Continued here.
– – –
Study: Recent enhanced high-summer North Atlantic Jet variability emerges from three-century context

Comments
  1. oldbrew says:

    From the study:

    An exceptional number of mid-latitude extreme weather events over the last decade has encouraged a suite of observational and modeling studies investigating the relative role of anthropogenic climate forcing and natural variability in driving this recent increase in weather extremes. One hypothesis suggests variability in the amplitude and speed of the Northern Hemisphere jet stream as a potential mechanism linking recent mid-latitude weather extremes to anthropogenic warming. This hypothesis is largely based on statistical associations between observational or atmospheric reanalysis data that are supported by plausible physical mechanisms. However, the data sets most frequently used provide relatively short time series (1979–present for the satellite era, 1948–present for the reanalysis era) that do not warrant robust results from a statistical significance perspective and that hamper the detection of non-linear relationships in a complex climate system. Long-term records of jet stream variability are thus needed to put recent trends in a historical perspective and to investigate non-linear relationships between jet stream variability, mid-latitude extreme weather events, and anthropogenic climate change. [bold added]

  2. Roger,

    I just read the title and something seems a bit odd.

    When I grew up in Southwestern Virginia, 1960 is the year I recall with the most snow. Starting in the middle of February, It snowed every Wednesday for five weeks and once on Saturday in between. We missed more school that year than ever. My wife grew up in Houston Texas and the February snow hit them before it hit us in Virginia.

    That being said, we have warmed out of the little ice age because it does not snow enough in cold times to maintain the ice volume necessary to stay cold. We are warmer now and it is snowing more now and the ice is being replenished. Open, Thawed, Arctic, vs Closed, Frozen Arctic should certainly promote different jet streams.

    You should read papers by Judah Cohen. He uses open Arctic and early snowfall to forecast the longer term weather in his long range forecasts.

    http://www.judahcohen.org/research-papers/

    I have been reading papers by Cohen and exchanging occasional email with him after seeing a story about his amazing forecasts on a show with Frank Billingsley, a lead Houston TV forecaster. I have exchanged emails with Frank and Judah since the show in 2011. I used to have a link the archives for that show on my website, but the TV station lost it when they rehosted their archives. Frank Billingsley actually came to one of my Climate lectures. Off the record, he said my theory is right.

    A lot of weather forecasters do not promote manmade warming on their shows. They also don’t talk against it because they work for media companies that would likely fire them if they did.

    Open Arctic should be used to forecast the next Little Ice Age. The Arctic was open during the Medieval Warm Period when the Vikings settled in Greenland, The Chinease mapped the Arctic during that time because it was open. The snow fell then to bring on the Little Ice Age. Study history and ice core data to better understand the ice cycles.

    Alex

  3. TA says:

    The jet streams are not static, they change shape and position constantly, so I don’t see how this study can track the position of the jet stream to the accuracy claimed, especially using tree rings.

    The dip in the jet stream that brought cold air to the eastern U.S. is now rotating to the east and taking the cold weather with it and bringing in the warm air behind it. How are you going to track movement like that using tree rings.

    Making claims about the jet stream are highly suspect considering the lack of a historical record. We don’t know if it is doing anything unprecedented or not.

  4. Stephen Richards says:

    This is childish. We have known for decades that the jetstreams guide the lows around the temperate zones of the planet. What is more important and more difficult to find is what drives the position of the Jetstream. Yes it is thought to be ocean temperatures but how and why?

  5. Claudius Denk says:

    Stephen Richards:
    What is more important and more difficult to find is what drives the position of the Jetstream. Yes it is thought to be ocean temperatures but how and why?

    Well stated. The answer to your question is boundary layers between moist and dry air, which become more substantial during warm, calm weather. Vortices (which provide a slick inner surface to facilitate flow) get their energy from the jet streams. But they get their substance from smooth, extensiive boundary layers between moist and dry air lower in the atmosphere. Thus the build up of boundary layers during warm, calm conditions creates the pathways for vortices and the jet streams. This is why ocean temperatures anticipate jetstreams.

    The ‘Missing Link’ of Meteorology’s Theory of Storms
    http://www.thunderbolts.info/forum/phpBB3/viewtopic.php?f=10&t=16329

    James McGinn / Solving Tornadoes

  6. craigm350 says:

    Reblogged this on WeatherAction News and commented:
    What at first sounds interesting hides some Mannian Frankenstein stitching;
    The unprecedented character of the late twentieth century increase is independent of reconstruction scaling period (Supplementary Fig. 8), but we recognize that our NAJ reconstruction ends in 1978 and thus does not itself register the increase.
    https://www.nature.com/articles/s41467-017-02699-3
    I’ll go back to reading Hubert Lamb 😂

  7. oldbrew says:

    TA says: Making claims about the jet stream are highly suspect considering the lack of a historical record. We don’t know if it is doing anything unprecedented or not.

    The researchers are trying to do that…

    Study: Here we combine two tree-ring records from the British Isles and the northeastern Mediterranean to reconstruct variability in the latitudinal position of the high-summer North Atlantic Jet (NAJ) back to 1725 CE.

    Any claims about recent ‘anthropogenic’ this-that-or-the-other are speculative and/or designed to appeal to reviewers IMO.

  8. Phoenix44 says:

    “We find that the position of the North Atlantic Jet in summer has been a strong driver of climate extremes in Europe for the last 300 years,” Trouet said.

    But they can’t possibly do that. They have to assume their conclusion – that the jet stream drives the extremes – to “know” where the jet stream was.

    If the extremes were caused by something else, then they don’t know where the jet stream was.

  9. p.g.sharrow says:

    Low pressure areas can not guide the jet streams. Loopiness is caused by high pressure areas diverting the air flow, this results in low pressure areas on the rebound. The over all Jet stream track moves North or South dependent on the overall strength of the Subtropic Hadley Cells. Which determine how tightly the Polar Vortex is confined….pg

  10. oldbrew says:

    ‘300 years of high-summer NAJ variability

    The reconstruction shows that late twentieth century NAJ positions fall within the latitudinal NAJ range of the preceding centuries, with the exception of the summer of 1976, which was the northernmost NAJ position in both the instrumental data and the reconstruction.’
    – – –
    Summer of ’76 – that was the hottest for the longest, in the UK at least.
    http://en.wikipedia.org/wiki/1976_United_Kingdom_heat_wave

    NAJ position correlates.

  11. Kip Hansen says:

    oldbrew ==> Tree ring barometers now? Or Tree Ring Jet Stream Detectors? When the rubber hits the road, they are measuring width of tree rings and guessing at something……

  12. oldbrew says:

    See ‘Reconstruction’ in the paper.

  13. erl happ says:

    PG Sharrow, you write “Low pressure areas can not guide the jet streams. “Loopiness is caused by high pressure areas diverting the air flow, this results in low pressure areas on the rebound. The over all Jet stream track moves North or South dependent on the overall strength of the Subtropic Hadley Cells. Which determine how tightly the Polar Vortex is confined….pg”
    I respectfully disagree. The ‘annular modes’ phenomenon is recognised as the prime mode of natural climate variation globally. It involves an exchange of atmospheric mass between the low-pressure cells at 60° -70° of latitude, especially in the southern hemisphere and other latitudes including across the hemispheres. The most energetic exchange is between 60-70° south latitude and 20-40° south. latitude.
    Over the last seventy years, reanalysis informs us of a loss of atmospheric pressure at 60-70° south of about 15 hPa. This is where the loss is most extreme. The gain in atmospheric pressure elsewhere is minute in comparison but it is greatest at 20-40latitude.
    In terms of causation you have the cart leading the horse. Let me explain.
    The annular modes phenomenon is driven from the winter hemisphere. It is driven by the absorption of long wave radiation from the earth itself. by ozone in the 9-10um wave length at a time when there is seasonal peak in ozone partial pressure outside the polar vortex (itself a winter phenomenon) and a seasonal trough in ozone partial pressure inside the vortex. The edge of the vortex is the jet stream. The vortex is in fact a chain of low pressure cells energised by air density contrast that is most extreme between the 100hPa and 50hPa atmospheric pressure intervals. That’s where the velocity of air movement is most extreme. It’s not low-pressure cells that ‘steer the jet stream’. The low-pressure cells are a product of forces in the stratosphere. In winter, In winter the margin between the so called troposphere and the stratosphere descends to 4-6km in elevation.It’s the forces in the stratosphere that create the low pressure cells. The weakest winds inside these cells are below 500 hPa. In effect the top half of the atmosphere, in terms of molecular mass, is stratosphere at that time.
    In discerning cause and effect, it pays to look at where the phenomena exhibit their most extreme characteristics….in this case its wind velocity allied with and driven by change in atmospheric pressure. All generated from what we call ‘the stratosphere’ rather than the troposphere that becomes the ‘active sphere’. The stratosphere near the poles in winter is a very different kettle of fish to what we observe in the tropics.
    The entire atmosphere, near ground level, in both hemispheres feeds an atmospheric sink on the margins of Antarctica. This is the big picture. It is the fluctuations in the strength of this sink that gives rise to variations in the strength of the winds in the Roaring Forties, the Furious Fifties and the Screaming Sixties. North of the sink the transfer of warmth from Equatorial latitudes to mid and high latitudes has been enhanced. So the climate has warmed. South of the sink the climate has cooled with an extension of already highly frozen winter temperatures into spring and summer. As the sink intensifies the outflow of very cold air from the Antarctic interior increases, limited in its northward travel by the ‘sink’ on the margins of the continent.
    Trouet et al, considering the effect of changes in the jet stream are exploring phenomena well recognised before it became fashionable and remunerative to talk about the impact of man on ‘the climate’. The pattern of climate change varies according to latitude and season according to what we recognise as ‘the annular modes phenomenon’. Annular means ‘ring like’.
    To get to the root of the phenomenon in the northern hemisphere they need to transfer their attention to the southern hemisphere.
    By virtue of the distribution of land and sea in the northern hemisphere the annular modes phenomenon is only weakly expressed there. It follows that there is a fine balance that determines whether cold winds from the north or warm winds from the south prevail in the mid latitudes. The continents tend to host high pressure cells in winter and low-pressure cells form over the sea where the greatest ozone partial pressure exists aloft. That semi stationary arrangement can be disturbed or it can stick….the blocking phenomenon.
    This is, or should be, climate 101.

  14. oldbrew says:

    Erl H mentions ‘the blocking phenomenon’…

    UK Met Office: The Russian heatwave of summer 2010

    The heat wave was caused by a ‘blocking high’ situation. Every now and again an area of high pressure intensifies to the point that it can become difficult for low pressure systems to break it down. Blocking highs can persist for weeks or even months.

    http://www.metoffice.gov.uk/learning/learn-about-the-weather/weather-phenomena/case-studies/russian-heatwave

    Temperatures peaked in the low forties Celsius in some places, normally would be low 20s in July in Moscow.

    The photo below shows the same street in Moscow on the 17 June and 7 August 2010. What a contrast.
    https://www.metoffice.gov.uk/binaries/content/gallery/mohippo/images/migrated-image/c/summer_10_moscow_smog.jpg/

  15. oldbrew says:

    Jetstream Forecast

    The jetstream plays a large role when it comes to the weather across the UK, so from here you can view the latest jetstream forecast right out to 16 days in 3 hour timesteps.

    http://www.netweather.tv/charts-and-data/jetstream

    Includes an ‘interactive global jet stream forecast map’…

    [screenshot]

  16. oldbrew says:

    Two statements to consider:

    1) Having a 290-year record of the position of the jet stream let Trouet and her colleagues determine that swings between northern and southern positions of the jet became more frequent in the second half of the 20th century, she said.

    Since 1960 we get more years when the jet is in an extreme position”, Trouet said, adding that the increase is unprecedented.

    2) “This is a whole Sun phenomenon,” said Dave McComas, Ulysses solar wind instrument principal investigator, from Southwest Research Institute, San Antonio, US.

    “The entire Sun is blowing significantly less hard – about 20-25% less hard – than it was during the last solar minimum 10-15 years ago.

    “That’s a very significant change. In fact, the solar wind we’re seeing now is blowing the least hard we’ve see it for a prolonged time, since the start of those observations in the 1960s at the start of the space age.” [bold added]

    http://news.bbc.co.uk/1/hi/sci/tech/7632331.stm

  17. Jim says:

    You are still talking about wind and patterns. Missing the point, that to have a pattern, there must be an influence. One influence or input does not create a pattern. Or a blizzard. There are many. Just as a volcano does not create a pattern, it changes a pattern. A pattern was already there, just from something else. Now you have a new input, and a new result.
    Amazing. But, throw this into the machine. Earthquakes, movement, and man-made obstruction of wind movement, localized heating ( such as mirrors and solar cells ) and changing inputs.. the aging of the sources, how does that help or hinder the processes. Hmm?

  18. oldbrew says:

    The solar wind isn’t really a wind, it’s a stream of charged particles.
    http://www-spof.gsfc.nasa.gov/Education/wsolwind.html

  19. oldbrew says:

    Is Arctic warming behind year’s crazy winter weather?
    By EarthSky Voices in EARTH | HUMAN WORLD | January 13, 2018

    An atmospheric scientist who studies the Arctic explains why – because of global warming – the U.S. may be in for longer cold spells in the winter.
    . . .
    A warm, dry western North America occurring in combination with a cold, snowy east is not unusual, but the prevalence and persistence of this pattern in recent years have piqued the interests of climate researchers.

    The jet stream – a fast, upper-level river of wind that encircles the Northern Hemisphere – plays a critical role. When the jet stream swoops far north and south in a big wave, extreme conditions can result. During the past few weeks, a big swing northward, forming what’s called a “ridge” of persistent atmospheric pressure, persisted off the West Coast along with a deep southward dip, or a “trough,” over the East.

    http://earthsky.org/earth/arctic-warming-behind-crazy-winter-weather

  20. Paul Vaughan says:

    “A warm, dry western North America”

    ?? dry?
    It’s raining for weeks without relent.

    Language encumbers discussion of spatial pattern.
    Mature discussion of aggregation criteria has not yet entered climate discussion.

    The major western fault has successfully built in delays.

  21. E.M.Smith says:

    On the question of low vs. high pressure steering things:

    My assertion is that pressure differential drives things.

    it matters not if the differential increases from higher highs or lower lows. Suck harder or blow harder both move more air.

    It may be convenient to think of one as causal IF the thing actually changing pressures drives it more; but the fundamental property of fluids will cause more flow with more differential regardless of which end of the pipe changes. (though clearly vacuum sets a lower bound while the upper bound is not so limited.)

  22. erl happ says:

    EM Smith. The questions is: Why and how does the differential change?

  23. p.g.sharrow says:

    As someone that has had to design and build pipe and duct lines for handling fluid flow, I can assure you it does make a difference whether they are pushed or pulled thru the conveyance, specially at turns and past obstructions. pushed flow tends toward the outside of the turn and builds turbulence at obstructions. Pulled flows tend to the inside of the turn and reduces turbulence going past obstructions. Whether you are adding or subtracting energy of a fluid in the overall flow direction does make a difference in the characteristics of the flow…pg

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