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The findings may help in predicting weather, especially for the northern hemisphere |
A new study
shows periods of low solar radiation could cause colder winters in northern
Europe and the continental United States, helping to explain recent cold
winters there despite growing greenhouse gas emissions.
Cyclical changes
in the amount of radiation emitted from the sun affect weather patterns in the
northern hemisphere, according to a study published on Monday in the journal
Nature Geoscience.
Researchers
analyzed recent satellite data to conclude that when ultraviolet emissions from
the sun drop, parts of Europe and North America experience harsher winters.
Sunspot
cycles
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Bitter weather caused chaos on the eastern seaboard last winter |
Scientists
have known for some time that radiation from the sun peaks and falls in a cycle
that runs around 10 or 11 years.
Sunspots
are an indicator of solar activity, and ultraviolet radiation varies in concert
with these cycles of activity.
The new
study relies on fresh data that suggests this activity is more variable than
previously thought.
"We're
actually measuring the direct amount of ultraviolet radiation that's reaching
the Earth," said Jeff Knight of the Met Office Hadley Centre in Exeter,
one of the study's authors.
The
scientists found that a reduction in ultraviolet light from the sun makes cold
air form in the atmosphere about 40 kilometers above the tropics.
"It
kicks off a chain of influences that lead to a reduction of the westerly winds
that blow across the Atlantic into Europe in the winter," Knight told
Deutsche Welle.
In a normal
winter, Europe receives westerly winds that cause a warming influence.
"When
we lose those winds, you lose that warming influence, bringing that cold,
Siberian-type of wind into northern Europe," Knight said.
These
frigid winds are part of a larger circulation that reaches all the way across
the Atlantic Ocean, to the Eastern seaboard of the United States. "So you
get similar types of weather in that region too – as demonstrated last
winter," Knight said.
During this
time of absent westerly winds, Canada and the Mediterranean experience milder
weather.
Periods of
stronger solar radiation, the scientists believe, cause the opposite effect.
Predicting
the weather
The study
could assist long-term predictions for winter weather around the world by
helping illuminate the sun's impact on climate.
"We
can't draw a direct one-to-one parallel between the sun and our weather – it's
more complicated," Knight said.
He added
that the study has more relevance for the northern hemisphere and mid-latitudes
of the Earth.
Some
skeptics of man-made global warming have pointed to variations in solar
activity as an alternative explanation for climate change.
Knight said
the new study did not challenge the role of greenhouse gases in affecting the
climate.
"This
study doesn't say anything at all about global climate," Knight
emphasized. "Air is being moved around, not changed – it's just a
rearrangement."
Knight said
he and other researchers planned to look into speculation that the sun may be
entering a period of prolonged relative inactivity, like what happened during
the "little ice age," between the 16th and 19th centuries.
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NASA captured this image of a solar flare on the Sun in 2008 |
Satellite
data
The study
was made possible thanks to new satellite data from 2004 that has been able to
measure the ultra violate radiation levels more accurately than before.
The
researchers ran the new data through computer models that simulate interactions
between the atmosphere and the ocean. Their findings were able to account for
the extreme winters experienced in parts of Europe and North America in recent
years.
The
relatively small size of the data sample spells a potentially high rate of
statistical uncertainty. The scientists hope to complete further studies as
more data become available.
The paper
involved five researchers with the Met Office (the UK public weather service),
one with the University of Oxford and the other with the University of London.
Author: Sonya Angelica Diehn
Editor: Nathan Witkop
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