A new teleconnection pattern emerges: the Arctic Dipole
OCEAN Newsletter Research Staff
Gordon Peabody, OCEAN Editor, Spring 2014
gordonpeabody@gmail.com
Editor’s note: This is part of our educational series on
Teleconnections: The study of connections between worldwide weather
systems. Matched pairs of High and Low Pressure, Ocean-Atmospheric
Systems around the world influence the location of our Jet Stream Storm
Track. These systems are referred to as “Oscillations” because they vary
between strong, Positive Phases and weak, Negative Phases.
In a 2008 article titled, Recent radical shifts of atmospheric circulations
and rapid changes in Arctic climate system Zhang et al. show that the
extreme loss of Arctic sea ice since 2001 has been accompanied by a
radical shift of the Arctic atmospheric circulation patterns, into a new
mode they call the Arctic Rapid change Pattern. The new atmospheric
circulation pattern has also been recognized by other researchers, who
refer to it as the Arctic Dipole (Richter-Menge et al., 2009). The old
atmospheric patterns that controlled Arctic weather--the North Atlantic
Oscillation (NAO) and Arctic Oscillation (AO), which featured air flow
that tended to circle the pole, now alternate with the new Arctic Dipole
pattern. The Arctic Dipole pattern features anomalous high pressure on
the North American side of the Arctic, and low pressure on the Eurasian
side. This results in winds blowing more from south to north, increasing
transport of heat into the central Arctic Ocean. The Arctic Dipole pattern
occurred in all summer months of 2007 and helped support the record
2007 summer reduction in sea ice extent (Overland et al., 2008). Fall
2008 through spring 2009 featured the old AO pattern. The new Arctic
Dipole pattern re-appeared in June - July 2009, but the old AO pattern
dominated in August - September, resulting in greater sea ice extent
than in 2007 and 2008. The Arctic Dipole pattern was active again in
October, inactive in November, and is reasserting itself this December.
As a result, Arctic sea ice reached a new record minimum for a 10-day
period in early November, increased above record lows during late
November and early December, and appears poised again to reach a
new record minimum later this December (Figure 2).
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Figure 2. Sea ice extent in the Arctic for this year (blue line) compared
to the record low year of 2007 (green line) and 1979 - 2000 average
(gray line). One could make the ice loss looks less significant by using
the full satellite data record from 1979 - 2008 for the average. Image
credit: National Snow and Ice Data Center.
Arctic Dipole blamed for colder winters in East Asia
It turns out that the new Arctic circulation patterns help to intensify the
Siberian High, a large semi-permanent region of surface high pressure
prevalent in winter over Siberia. According to Honda et al. (2009), this
results in increased flow of cold air out of the Arctic in early winter over
eastern Russia, Japan, Korea, and eastern China, causing colder
temperatures. By late winter, the pattern shifts, resulting in colder than
average temperatures from East Asia to Europe.
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Arctic Dipole blamed for drier winters in Northern Europe
Francis et al. (2009) found that during 1979 - 2006, years that had
unusually low summertime Arctic sea had a 10 - 20% reduction in the
temperature difference between the Equator and North Pole. This
resulted in a weaker jet stream with slower winds that lasted a full six
months, through fall and winter. The weaker jet caused a weaker
Aleutian Low and Icelandic Low during the winter, resulting in a more
negative North Atlantic Oscillation--a pattern that usually brings
reduced winter precipitation over Alaska and Northern Europe and
increased precipitation over Southern Europe. A more negative NAO
also tends to bring cold winters to eastern North America and Europe.
Though it was not mentioned in the article, reduced Arctic sea ice may
also cause dry early winter conditions in the U.S. and the Caribbean
(Figure 3). The authors noted that strong La Niña or El Niño events can
have a much larger influence on the wintertime atmospheric circulation,
which will overshadow the changes due to Arctic sea ice loss.
Commentary
Arctic sea ice loss appears to have created a new atmospheric
circulation pattern that brings more warm air in the Arctic, creating a
positive feedback loop that causes even more sea ice loss. This feedback
loop increases the likelihood that an ice-free Arctic in the summer will
indeed come by 2030, as many Arctic experts are predicting. It's worth
noting that such an atmospheric circulation shift was not predicted by
the climate models. Indeed, the loss of Arctic sea ice over the past three
years exceeds what any of our models were predicting (Figure 4). While
we can rightly criticize these models for their inaccuracy, we should
realize that they are just as capable of making errors not in our favor as
they are of making errors in our favor.
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Figure 3. Difference in early winter precipitation (November - January)
between five years that had low Arctic sea ice (2005, 2006, 2007, 2008,
and 2009), and five years that had unusually high Arctic sea ice extent
(1981, 1984, 1986, 1989, 1993). Note that low sea ice may be
responsible for dry conditions in early winter for the Caribbean and
most of the U.S.
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http://www.youtube.com/watch?v=p_uqPR4Ir5o&feature=youtube_gdata_player
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