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Pollution bringing stronger cyclones
NEWS BRIEFS
30 years. None had occurred during
the monsoon season, and before 1998,
cyclones in the months before and after
that rainy season seldom reached wind
speeds exceeding about 80 kilometers per
hour. But since then, five monster storms
reached wind speeds double the norm.
After poring over weather data for
the period, the researchers found that
in premonsoon months there had been
a slow relaxation in the average vertical
wind shear, from 11 meters per second
to 8 meters per second.
That lower speed appears
to represent some type
of threshold, Evan says:
Once vertical wind
shears reach it, there’s
an explosion in storm
intensities, he says.
By Janet Raloff
A large and growing brown cloud
of persistent air pollution hovering
over northern India and surrounding
regions has doubled—and occasionally tripled — the intensity of late spring
cyclones in the Arabian Sea during the
last three decades.
Within the last decade, several early-season tropical cyclones have ripped
through the region.
Gonu, the strongest,
smashed through the
Middle East in 2007,
killing dozens and causing more than $4 billion
worth of damage.
These big storms,
which invariably make
landfall, represent a new
environmental impact
that can wreak havoc on
people from northern
India through the Middle East, climate scientist Amato Evan of the
University of Virginia in
Cyclone Gonu, seen here
in June 2007, produced
Category 5 winds before
hitting Oman and Iran.
Charlottesville and his
colleagues propose in the Nov. 3 Nature.
Warming sea-surface temperatures
can boost the intensity of hurricanes,
known in the Indian Ocean as cyclones.
And for many decades, Evan says, water
in the Arabian Sea has been “really
toasty.” But winds in the upper and lower
atmosphere there tend to blow briskly in
opposing directions, in a phenomenon
known as vertical wind shear. “This is
the most hostile environment one could
imagine for a hurricane,” Evan explains.
“It literally tears a storm apart.” That
appears to explain why major cyclones
here were rare — until recently.
The researchers ultimately linked the steady
fall in vertical wind
shear in cyclone seasons
with a 3-kilometer-thick
brown cloud of soot and
other pollutant particles,
known as aerosols, in
the region’s lower atmosphere. This pollution
has increased sixfold in 80 years, the scientists report, and now prevents roughly
10 percent of sunlight from reaching
the sea surface.
Evan and his team analyzed every
regional tropical cyclone going back
Computer analyses indicate that the
pollution cloud’s cooling effect on the
ocean below has slowed wind speeds in
the atmosphere —and allowed storm
intensities to mushroom. “This link to the
brown cloud is quite robust,” Evan says.
Evan and his team don’t have many
storms on which to base this claim
of a regional shift in climate signals,
says Ryan Sriver of Pennsylvania State
University in University Park. “But then,
I’m skeptical of everything,” he says.
“They do appear to have pretty strong
evidence.” s
Brush with tsunami protection
Coastal vegetation, often touted
as a buffer against extreme waves,
really can save lives during a
tsunami, a new paper suggests.
Scientists from the University of
Hohenheim in Germany and the
World agroforestry Centre in Bogor,
Indonesia, analyzed 180 cross
sections of the coastal landscape
in aceh, Indonesia —a region
devastated by the 2004 Indian
Ocean tsunami. Other factors
being equal, having trees or
shrubs between a village and the
coast can reduce casualties by
an average of 5 percent, the team
reports online november 7 in
the Proceedings of the National
Academy of Sciences.
—Alexandra Witze
Microbes’ hotter job market
Microbes are important in releasing stored nutrients from frozen
soils into the warming atmosphere.
as frozen soil thaws, so too do the
microbes within —genes and all.
a team led by Janet Jansson of the
Joint Genome Institute in Walnut
Creek, Calif., and the Lawrence
Berkeley national Laboratory has
warmed up samples of alaskan
permafrost and watched how the
genetic activity of the critters living
within changed. When warmer,
microbes altered the way they
cycled key elements such as carbon and nitrogen, the researchers
report online november 6 in
Nature. as part of the work, the
team pieced together the genome
of a methane-munching bug never
before seen, the first time such a
complex soil organism has been
assembled in such a way.
—Alexandra Witze
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December 17, 2011 | SCIENCE NEWS | 13
