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Earth Science Lecture ESC1000
A Wacky Jet Stream is Making Our Weather Severe
Scientific American December 2014
Read A Wacky Jet Stream is Making Our Weather Severe, then answer the questions
below. Print your document and submit a hard copy by the deadline given in the schedule.
This article discusses the causes and affects of the jet stream. The article was published in
Scientific American, December 2014 written by Jeff Masters (director of meteorology at
Weather Underground). A pdf version of the article is in the Assignments folder in
Canvas: A Wacky Jet Stream is Making Our Weather Severe. It is provided for this classes
access the text only version of this article online via the HCC library website.
For further reading also see: http://www.bbc.com/news/science--environment--26023166
1. The page titled How it Works, main image of the Earth (viewing the northern
hemisphere Americas), shows the atmospheric circulation pattern of the Earth in
both the horizontal and vertical sense.
a. Red arrows show the surface level winds. What are these three wind belts
called? List them from north to south order. (6 pts.)
b. Draw a map view diagram of the Earth and mark on and label these wind
patterns for the northern hemisphere only (divide the hemisphere into 30
degree belts or zones). (4 pts.)
c. The diagram also indicates the circulatory cells (Polar, Ferrell, and Hadley)
movement of air in the vertical sense. What are the three basic
climate/vegetation patterns that result at the boundaries between these
cells at the equator, at 30 degrees north and at 60 degrees north? (6 pts.)
2. Why waviness Changes: Two Possibilities numbered 1 and 2 (red numerals in
yellow circles) section.
Earth Science Lecture ESC1000
a. Panel 1, Atmospheric Oscillations considers natural explanations for
changes in the jet stream based on changes in what? (4 pts.)
b. Panel 2, Arctic Amplification considers the role of sea--ice. How does the
amount of sea--ice cover (in the Arctic) effect the atmosphere? (6 pts.)
c. Is the reduction in sea--ice likely to lead to further sea--ice loss why? (6 pts.)
3. The upper right section of Panel 1 Arctic Oscillation illustrates a positive phase and
a negative phase.
a. What distinguishes the two phases i.e. what is different? (6 pts.)
4. If the warming trend in global average temperatures continues what will the likely
effect be on the jet stream? (2 pts.)
5. According to the article what is the greatest threat to humans as a result of our
changing weather patterns? Why is this considered the greatest threat? (6 pts.)
6. What does waviness of the jet stream remind you of? Something we learned about
in the hydrosphere section of the course. What is the consistent factor between the
two phenomena? (4 pts)
waves froze this lighthouse
in Michigan during a harsh
68 Scientific American, December 2014
10/22/14 2:25 PM
c l i m at e
Extreme summers and winters
of the past four years
THOMAS ZAKOWSKI Landov
could become the norm
By Jeff Masters
December 2014, ScientificAmerican.com 69
10/21/14 3:17 PM
Je? Masters is director of meteorology at the Weather
Underground, which he co-founded in 1995, and specializes
in severe weather forecasting. He also writes WunderBlog,
one of the most popular weather blogs on the Internet.
ROM NOVEMBER 2013 THROUGH JANUARY 2014, THE JET STREAM TOOK ON A REMARKABLY EXTREME AND PERSISTENT
shape over North America and Europe. This global river of eastward-flowing winds high in the atmosphere dipped farther south than usual across the eastern U.S., allowing the notorious polar vortex of
frigid air swirling over the Arctic to plunge southward, putting the eastern two thirds of the country into
a deep freeze. Ice cover on the Great Lakes reached its second-greatest extent on record, and two crippling snow-and-ice storms shut down Atlanta for multiple days.
At the same time, a stubborn ridge of high pressure hunkered
down over California, creating the warmest winter on record
there. Although the balminess may sound nice, the resulting
drought became the worst since record keeping began in the
late 1800s, causing billions of dollars in agricultural losses.
The jet streams contortions also pummeled Europe, where a
succession of intense storms led to additional billions of dollars
of damage. In England and Wales the winter was the wettest
since at least 1766. Much of the rest of Europe basked in exceptional warmth: Norway suffered unprecedented January wildfires, and Winter Olympics officials in Sochi, Russia, struggled
with melting ski slopes. In May nearly one third of the entire
country of Bosnia was flooded by a massive, swirling rainstorm.
Ordinarily the jet stream resembles a band of air blowing
across the middle latitudes. As we see on television weather
forecasts, it often has mild bends from north to south and back
to north again, looking somewhat like a sine wave on an oscilloscope. The bends are called planetary or Rossby waves and
typically progress across the U.S. in three to five days. They
deliver much of the day-to-day weather we experience.
During the 20132014 winter, however, the waves became amplified with gigantic, steep sides, resembling an erratic electrocardiogram printout. This configuration of winds also moved
across the earth much more slowly than usual, at times stopping
in place for weeks and bringing remarkably long periods of uncommon weather. A May study led by Shih-Yu (Simon) Wang of
Utah State University found the jet stream pattern over North
America during that time was the most extreme ever recorded.
Was the radical jet stream an anomaly? Apparently not, because it seems to be happening more and more. In 2010 Russia
baked through its most oppressive heat wave in written history,
one that killed more than 55,000 people. At the same time, intense rains deluged Pakistan, its most expensive natural disaster
on record. In 2011 Oklahoma endured the hottest summer any
American state has ever had. U.S. drought conditions in 2012
were the most extensive since the 1930s.
The bends in the jet stream during those particular events
shared a common feature, according to an April 2013 paper by
scientists at the Potsdam Institute for Climate Impact Research
in Germany, led by Vladimir Petoukhov. The usually eastwardmoving waves ground to a halt and were greatly amplified,
two of the authors wrote in a blog post about their research. In
some cases, the bends remained stuck for days or even months
at a time. The scientists also showed that the extreme configurations were twice as common during summers from 2001 to
2012 as they were during summers of the prior 22 years.
As Bob Dylan sang, You dont need a weatherman to know
which way the wind blows. Something is clearly up with the jet
stream, and it is not hard to see the probable reason why. The
base state of our climate has changed dramatically over the past
150 years, and that change is starting to alter the jet streams
behavior. Atmospheric levels of heat-trapping carbon dioxide,
for example, have increased more than 40 percent, primarily
because of the burning of coal, oil and natural gas. The extent of
summer sea ice in the Arctic is down nearly 50 percent since
1900, affecting heat flow in the atmosphere and ocean. Solar
energy reflecting off the earths surface has changed significantly
because we have modified more than half of the planets landscape with crops, pastures and cities. Massive clouds of sunlightreflecting and sunlight-absorbing soot and pollution belch forth
Severe weather outbreaks have occurred in the past four years when the jet
stream has become contorted into extreme positions.
Extended bouts of outlandish weather
have taken place when the jet stream
has become stalled in these shapes for
Some scientists assert that the leading cause of a weird jet stream is the
loss of Arctic sea ice, although other experts disagree.
Either way a more extreme jet stream
will mean greater droughts, ?oods, heat
waves and deep freezes in many parts
of the world.
70 Scientific American, December 2014
10/21/14 3:17 PM
High-Altitude clouds, as seen from the Space Shuttle, gather along the jet stream over eastern Canada. North is toward
the bottom of the image, where Cape Breton Island is visible ( center ). The jets speed can top 300 kilometers per hour.
from power plants, vehicles, buildings and industries. A huge
ozone hole disrupts upper-level winds over the Antarctic.
Humans have kicked the climate system hard, and physics
demands that the earths fundamental weather patterns change
as a result. Indeed, Wang and his colleagues concluded that the
jet streams configuration most likely could not have grown so
strange without the influence of human-caused global warming.
The danger is that climate is not linear. A modest level of global warming can suddenly create a step change to a new regime
with wildly different weather. Climate scientists are intensely
debating whether climate as a whole and the jet stream in particular have crossed a tipping point into a new long-term state.
They are also debating a controversial theory put forth by the
Potsdam researchers and others that says that the changes in
the jet stream stem largely from events occurring in the fastestwarming portion of the planetthe Arctic.
If indeed the jet stream is entering a new state, that bodes ill
for civilization. An August paper published in Nature Climate
Change by James Screen of the University of Exeter in England
and Ian Simmonds of the University of Melbourne in Australia
went so far as to pinpoint the potential effects. ( Scientific American is part of Nature Publishing Group.) If jet stream waves are
amplified in response to anthropogenic [human-caused] climate
change, as has been proposed, they wrote, our results suggest
that this would preferentially increase the probabilities of heat
waves in western North America and central Asia, cold waves in
eastern North America, droughts in central North America,
Europe and central Asia, and wet extremes in western Asia.
This new normal would mean more terrible summer droughts
for midwesterners. Winters featuring strings of snowstorms like
the 2010 snowmageddon that closed Washington, D.C., would
blast eastern U.S. residents more often. And people worldwide
would see food prices go up, a consequence of intense and persistent droughts in central North America, Europe and Central Asia.
Climate change would revise the jet stream indirectly by acting
on big forces in the atmosphere that ultimately shape it. The
ever present river of wind, nine to 14 kilometers high, circles
the globe in both hemispheres and acts as a guide along which
precipitation-bearing low-pressure systems ride. The jet stream
typically has two branches: a polar jet that acts as the boundary
between cold air near the poles and warm air closer to the equator and a less vigorous subtropical jet that lies closer to the equator. Henceforth, when I discuss the jet stream, I mean the dominant polar jet.
That jets latitude rises and falls a bit with the seasons: it is
typically over the central U.S. in winter and near the U.S.-Cana-
December 2014, ScientificAmerican.com 71
10/21/14 3:17 PM
H OW I T WO R K S
A Radical Jet Stream Delivers Extreme Weather
Two jets of high-altitude wind blow around the earth in each hemisphere. When bends in the polar jet become magni?ed
(left-hand page), abnormally warm or cold air can wallop large regions of a continent. The bends can also get stuck that
way for weeks, causing droughts, ?oods, heat waves and deep freezes. Two leading theories can explain the big bends
(right-hand page), one driven by climate change and one linked to either climate change or natural variability.
Jet Streams Form
Because the equator gets more solar energy than the poles, hot air rises there,
hits the stratosphere and spreads toward the poles. The earths spin de?ects the
air into three major, interlocking atmospheric circulation cells in each hemisphere.
Jet streams arise along the cell boundaries to equalize pressure di?erences.
Waviness Brings Heat Waves and Deep Freezes
When mild bends in the polar jet stream become ampli?ed (wavy blue arrow),
huge warm-air masses can surge much farther north than usual, and cold-air
massessuch as the winter polar vortexcan plunge far to the south. The bends
typically progress across the U.S. in three to ?ve days, delivering our daily weather.
WARM AND DRY
COLD AND WET
bends, known as
Rossby waves, can get
stuck in place, locking
in long periods of
If the polar jet stream has crossed a tipping
point to a new state in which big bends
become common, the U.S. may see more
heat waves in the west, cold waves in the
east and drought in the central states.
10/21/14 3:17 PM
Why Waviness Changes: Two Possibilities
Positive phase is linked
to a large pressure
di?erence, which helps
the jet stream take
a straighter path,
and to a strong polar
vortex, which keeps
cold air north
Negative phase is linked
to a small pressure
weakens the jet stream
so big bends are more
likely, and weakens the
polar vortex, allowing
cold air to drift south
The Arctic is warming up two to three times as fast as the midlatitudes. Disappearing
sea ice (below) is a major reason: more exposed water absorbs extra solar heat in
summer and reradiates it in winter, raising air temperature in the polar cell faster
than the rise in the Ferrell cell (right). The declining di?erence between cells makes
a negative Arctic Oscillation and wavy jet stream (above right) more likely.
Faster autumn winds
1 degree C
Slower autumn winds
Less ice, less re?ection
Less Ice, Weaker Winds
From 1979 to 2012 the minimum area
of Arctic sea ice dropped 40 percent,
and autumn winds high over North
America slowed 10 percent (graphs).
Slower winds are associated with big,
problematic bends in the jet stream.
More heat a
Decreased sea-ice area
Slower high-altitude winds
Illustration by Juan Velasco (5W Infographics), Research by Amanda Hobbs
More ice, more re?ection
Week-to-week changes in sea-level
pressure between the Arctic and
midlatitudes cause this phenomenon;
factors not fully understood shift it
between positive and negative phases.
El Niño/Southern Oscillation
This cycle in tropical atmospheric pressure has two phases:
El Niño brings warmer Paci?c Ocean water eastward, moving
the jet stream south; La Niña brings cooler water, moving
the jet north. Recent, large di?erences in the phases, linked
to a wavy jet, may be natural or driven by climate change.
SOURCE: NATIONAL CENTERS FOR ENVIRONMENTAL PREDICTION AND EARTH SYSTEM RESEARCH LABORATORY (bottom right charts, wind
data), NATIONAL SNOW AND ICE DATA CENTER (bottom right charts, sea ice data), COMPILED BY DR. JENNIFER FRANCIS (bottom right charts)
Natural phenomena in the atmosphere can alter the jet streams path. Two prime
suspects are the El Niño/Southern Oscillation and the Arctic Oscillation.
December 2014, ScientificAmerican.com 73
10/21/14 3:18 PM
dian border in summer. The flow, however, is chaotic, and large
Rossby waves are always present. In the Northern Hemisphere,
when the jet stream bulges northward as a ridge of high pressure,
warm air flows up from south to north. Where the jet loops to the
south as a trough of low pressure, cold air spills southward.
The jet stream is created by three major interlocking cells of
circulating air over each hemisphere [ see box on two preceding
pages ]. Although the cells help to shape the jet stream, other
forces in the sky can contort it further. The atmosphere actually resonates because of energy from the sun, the shape and
location of the continents and ocean currents, the presence of
mountain ranges, and the amount of heat-trapping greenhouse
gases and reflective dust in the air. Just as a guitar resonates
differently when various strings are plucked, as these factors
change, the atmosphere resonates with multiple tones, called
teleconnection patterns. These na …
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