[Vision2020] PNAS: Arctic Sea Ice Decline May Be Driving Snowy Winters in N. Hemisphere

[Ted Moffett]

Proceedings of the National Academy of Sciences

http://www.pnas.org/content/early/2012/02/17/1114910109

Impact of declining Arctic sea ice on winter snowfall

Jiping Liua,b,1, Judith A. Currya, Huijun Wangb, Mirong Songb, and
Radley M. Hortonc
+ Author Affiliations

aSchool of Earth and Atmospheric Sciences, Georgia Institute of
Technology, Atlanta, GA 30332;
bLASG, Institute of Atmospheric Physics, Chinese Academy of Sciences,
Beijing, 100029, China; and
cColumbia University Center for Climate Systems Research, New York, NY, 10025
Edited by Mark H. Thiemens, University of California San Diego, La
Jolla, CA, and approved January 17, 2012 (received for review
September 9, 2011)

Abstract

While the Arctic region has been warming strongly in recent decades,
anomalously large snowfall in recent winters has affected large parts
of North America, Europe, and east Asia. Here we demonstrate that the
decrease in autumn Arctic sea ice area is linked to changes in the
winter Northern Hemisphere atmospheric circulation that have some
resemblance to the negative phase of the winter Arctic oscillation.
However, the atmospheric circulation change linked to the reduction of
sea ice shows much broader meridional meanders in midlatitudes and
clearly different interannual variability than the classical Arctic
oscillation. This circulation change results in more frequent episodes
of blocking patterns that lead to increased cold surges over large
parts of northern continents. Moreover, the increase in atmospheric
water vapor content in the Arctic region during late autumn and winter
driven locally by the reduction of sea ice provides enhanced moisture
sources, supporting increased heavy snowfall in Europe during early
winter and the northeastern and midwestern United States during
winter. We conclude that the recent decline of Arctic sea ice has
played a critical role in recent cold and snowy winters.
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http://www.sciencedaily.com/releases/2012/02/120227111052.htm

Unusual Weather: Arctic Sea Ice Decline May Be Driving Snowy Winters
Seen in Recent Years in N. Hemisphere

ScienceDaily (Feb. 27, 2012) — A new study led by the Georgia
Institute of Technology provides further evidence of a relationship
between melting ice in the Arctic regions and widespread cold
outbreaks in the Northern Hemisphere. The study's findings could be
used to improve seasonal forecasting of snow and temperature anomalies
across northern continents

Since the level of Arctic sea ice set a new record low in 2007,
significantly above-normal winter snow cover has been seen in large
parts of the northern United States, northwestern and central Europe,
and northern and central China. During the winters of 2009-2010 and
2010-2011, the Northern Hemisphere measured its second and third
largest snow cover levels on record.

"Our study demonstrates that the decrease in Arctic sea ice area is
linked to changes in the winter Northern Hemisphere atmospheric
circulation," said Judith Curry, chair of the School of Earth and
Atmospheric Sciences at Georgia Tech. "The circulation changes result
in more frequent episodes of atmospheric blocking patterns, which lead
to increased cold surges and snow over large parts of the northern
continents."

The study was published on Feb. 27, 2012 in the online early edition
of the journal Proceedings of the National Academy of Sciences.

In this study, scientists from Georgia Tech, the Chinese Academy of
Sciences and Columbia University expanded on previous research by
combining observational data and model simulations to explore the link
between unusually large snowfall amounts in the Northern Hemisphere in
recent winters and diminishing Arctic sea ice.

The researchers analyzed observational data collected between 1979 and
2010 and found that a decrease in autumn Arctic sea ice of 1 million
square kilometers -- the size of the surface area of Egypt --
corresponded to significantly above-normal winter snow cover in large
parts of the northern United States, northwestern and central Europe,
and northern and central China.

The analysis revealed two major factors that could be contributing to
the unusually large snowfall in recent winters -- changes in
atmospheric circulation and changes in atmospheric water vapor content
-- which are both linked to diminishing Arctic sea ice. Strong warming
in the Arctic through the late summer and autumn appears to be
enhancing the melting of sea ice.

"We think the recent snowy winters could be caused by the retreating
Arctic ice altering atmospheric circulation patterns by weakening
westerly winds, increasing the amplitude of the jet stream and
increasing the amount of moisture in the atmosphere," explained Jiping
Liu, a senior research scientist in the School of Earth and
Atmospheric Sciences at Georgia Tech. "These pattern changes enhance
blocking patterns that favor more frequent movement of cold air masses
to middle and lower latitudes, leading to increased heavy snowfall in
Europe and the Northeast and Midwest regions of the United States."

Diminishing Arctic sea ice can cause changes in atmospheric
circulation that lead to a circulation pattern that is different than
the "negative phase" of the Arctic Oscillation.

In addition to analyzing observational data, the researchers also
assessed the impact of the diminishing Arctic sea ice on atmospheric
circulation by comparing the results of model simulations run with
different sea ice distribution. They ran one experiment that assumed
seasonally varying Arctic sea ice and utilized sea ice concentration
data collected between 1979 and 2010. Another simulation incorporated
prescribed sea ice loss in autumn and winter based on
satellite-derived Arctic sea ice concentrations.

The simulations showed that diminishing Arctic sea ice induced a
significant surface warming in the Arctic Ocean and
Greenland/northeastern Canada, and cooling over northern North
America, Europe, Siberia and eastern Asia. The models also showed
above-normal winter snowfall in large parts of the northern United
States, central Europe, and northern and central China.

The consistent relationships seen in the model simulations and
observational data illustrate that the rapid loss of sea ice in summer
and delayed recovery of sea ice in autumn modulates snow cover, winter
temperature and the frequency of cold air outbreaks in northern
mid-latitudes.

Huijun Wang and Mirong Song of the Chinese Academy of Sciences
Institute of Atmospheric Physics and Radley Horton from the Columbia
University Center for Climate Systems Research also contributed to
this work.

This project was supported by the NASA Energy and Water Cycle Study
and the National Science Foundation (NSF) (Award No. ANT-0838920).

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Vision2020 Post: Ted Moffett