Vortex Spins up Wayward Jetsteam Discussion Again

July 18, 2014

Compare this image from last winter to the current ones below

John Abraham in The Guardian:

As I sit here in a northern part of the United States (Minnesota), a rare summer arctic blast barrels down from Canada on what otherwise is one of the warmest days of the year. Global warming? I could use some global warming today, people are saying.

Not only is this a teachable moment, but it coincides with a major new study on climate connections. First, let’s see the current jet stream. It is wildly undulating, first swinging up into northern Canada before curving back and plunging into the central United States.

Typically, the jet stream represents a separation between cold arctic air and warmer southern air. If you are north of the jet stream, temperatures are cold whereas south of the jet stream it’s more likely to be warm.

With this in mind, and the jet stream shown, you can almost predict the temperature pattern in the next image. The match is incredible and it is clear that my Minnesota cold-blast is more than balanced out by near 90°F temperatures in northern Canada. With all of this, I want to talk about a new study that looks at these fluctuations on a longer term.

Very recently, a paper Amplified mid-latitude planetary waves favor particular regional weather extremes was published in the journal Nature Climate Change. The authors, James Screen and Ian Simmonds, investigated the role that changes to upper level winds in the atmosphere have on the occurrence of extreme weather. What they found was very interesting.

The authors don’t ask the question “are humans changing the jet stream patterns?”. Instead, they ask, “how do undulations in the jet stream affect weather?”. To be fully accurate, the study isn’t just about jet streams, it really deals with mid-latitude planetary waves but for this article, I will use the term “jet stream” as a surrogate for simplicity.

The authors went back into our weather records (1979–2012) and found the 40 months with the most extreme weather (most extreme precipitation and most extreme temperatures). They then evaluated how “wavy” the jet stream was during those extreme months. They found that,

months of extreme weather over mid-latitudes are commonly accompanied by significantly amplified quasi-stationary mid-tropospheric planetary waves. Conversely, months of near average weather over mid-latitudes are often accompanied by significantly attenuated waves.

In common parlance, this means that when the jet stream undulates and travels very slowly, we see more extreme weather. Conversely, when the jet stream travels in a straighter path, the weather is less extreme.

Joe Romm in ClimateProgress:

“We’ve got this cool air coming down over the eastern half of the country, and that’s gonna just be kind of nice,” said Jennifer Francis, an atmospheric scientist and research professor at Rutgers University’s Institute of Marine and Coastal Sciences. “But along the east coast, we’re looking at storms and floods. On the west coast, we’re looking at heat and fires. And it’s all part of this jet stream pattern.”

A particularly wavy jet stream is what is causing the so-called “polar vortex,” or cold air from the Arctic, to travel down to the United States, Francis said. The dramatic and unusual southward swoop, shown in the map on the right, allows air from the cold north to travel south. The same thing happened this past January, when a dramatic southward swing of the jet stream brought increased cold air to an already-freezing region. That was big news, extreme weather-wise.

Now, the “polar vortex” is making for fairly mild weather. But at the same time, that same wavy jet stream is swinging northward in the western United States, bringing increased heat to an already-dry and wildfire-stricken region. Extreme weather-wise, Francis says, this is a bigger deal.

“They’re going to be suffering out there,” she said. “That part of the story is more important in a way because they’re already dealing with such a drought that this is just going make the drought and the fires and everything much worse, while in the east it’s just going to be a nice couple of cool days to break up the hot summer.”

As the jet stream dips upward following its southward travels, the east coast will also see some more newsworthy weather, Francis said. “That’s where it’s really stormy,” she said “You see storms and flooding on the east side of those southward dips.”

SkyNews on last winter’s Jet stream alignment:

ClimateProgress:

Weather forecasts are predicting thunderstorms and flash flooding up the East Coast this week, from Atlanta to New York.

This particularly wavy jet stream has been largely attributed to Japan’s typhoon Neoguri, the immense energy of which likely caused a swift acceleration of the North Pacific jet stream. Francis says to think of it like taking a jump rope and giving it a whip with your hand — except the jump rope is the jet stream, and your hand is a typhoon. The whip, intensified by your strength, travels along the rope with a ripple effect.

In addition to being powered by storms, though, the jet streams movements may be impacted by a warming Arctic. Francis’ research suggests that as the Arctic warms due to climate change, less drastic changes in temperatures occur between northern and southern climates. This leads to weakened west-to-east winds, and ultimately, a wavier jet stream.

“Our research suggests that these kinds of patterns where the jet stream is taking these big northward and southward swings is going to become more frequent in the future, at least partly related to the fact that the Arctic is warming so fast,” she said. “We can’t say that this particular example is related to the Arctic. That being said, the Arctic is very warm right now, and so it could be contributing to making this pattern more wavy than it would have been otherwise.”

Francis’ research on Arctic warming being connected to a wavier jet stream is still disputed. Dr. Kevin E. Trenberth, a distinguished senior climate scientist at the National Center for Atmospheric Research, told ClimateProgress in January that he was still skeptical of the connection. “[It] shows a correlation, but correlation is not causation,” hesaid at the time. In a recently published update on the linkage between Arctic warming and its impact on jet stream patterns, The National Research Council was optimistic about the connection, but noted it was still too early to draw concrete conclusions.

The weather the U.S. is experiencing now is the result of a similar offshoot of the Arctic jet stream that brought down the colder temperatures in January, though this week’s weather will include a good deal of northeast Pacific air, rather than just Arctic. As for whether both instances should really be called the “polar vortex,” Francis says no, saying it’s a mischaracterization of the term. Really, she said, the polar vortex refers to the whole Arctic jet stream taken together, not the actual cold air inside of it.

Takeaway:

More High amplitude fluctuations in the jet, which bring with them extreme events, i.e. sweater weather in July to Eastern North America, Hot, dry, wildfire weather to the northwest and canada.

General agreement that a wayward jet may be climate related, no agreement on exact mechanism.

6 Responses to “Vortex Spins up Wayward Jetsteam Discussion Again”

  1. rayduray Says:

    NASA’s Earth Observatory has a pair of images comparing California today to how much greener it was 3 years ago.

    http://earthobservatory.nasa.gov/IOTD/view.php?id=84032&eocn=home&eoci=iotd_image

    “The Golden-Brown State”

  2. climatebob Says:

    The test would be, if the jet stream gets stuck and keeps this pattern for weeks. We will have to wait and see. You might like my latest blog on IPCC and the climate. http://www.climateoutcome.kiwi.nz/blog

    • dumboldguy Says:

      Great commentary, and the two quotes are particularly good.

      Considering that Mike Tyson is not a climate scientist, he got it right with “Everyone has a plan until they get punched in the mouth”. Translated, that says “We have high hopes for renewables until the s**t hits the fan and we exceed the tipping points. Then we fight for our lives”

      The Rumsfeld corollary would then be, “Once the known unknowns become clearer and the unknown unknowns start to make themselves known, we can really make a plan (and hope it’s not too late)”


  3. […] Vortex Spins up Wayward Jetsteam Discussion Again […]

  4. dumboldguy Says:

    Good takeaway. Surprised no one wants to comment on this clip. Maybe it’s just so obvious what’s going on and what pattern seems to be repeating?

    Here on the east coast, we first had days of rain as the hot humid air masses rode up the eastern edge of the cold air mass—-lots of mushrooms sprouting and the grass staying green and growing when it should have been going into summer semi-dormancy.

    Once the “polar vortex” moved over us we had a series of beautiful low humidity and low temp days. Wife and I rode up to Shenandoah National Park one of those days to sightsee, and it was reminiscent of a summer day in Colorado.

    The road through the park and the campgrounds are at elevations of 3+ thousand feet and you would definitely have needed a sweater at night. Unusual for mid-July. I for one will welcome the cold air from the arctic in the summer if this pattern persists—-the D.C. area is hardly better than a tropical swamp much of the time.


  5. […] many of us in North America have noticed this summer, is that last winter’s atmospheric configuration, cool east, – hot, dry west, has […]


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