National Science
Foundation
Press Release 11-234
Link Between Air Pollution and
Cyclone Intensity in
Disruption of wind shear enables
stronger storms
http://www.nsf.gov/news/news_summ.jsp?cntn_id=122072&WT.mc_id=USNSF_51&WT.mc_ev=click
Pollution
is making
Traditionally,
prevailing wind shear patterns prohibit cyclones in the
The Nature paper suggests that weakening winds
have enabled the formation of stronger cyclones in recent years--including
storms in 2007 and 2010 that were the first recorded storms to enter the
Researchers
note that weakening wind patterns during the last 30 years correspond with
a buildup of aerosols in the atmosphere over
The
aerosol buildup creates formations known as atmospheric brown clouds (ABCs) in
which smog from diesel emissions, soot and other by-products of biomass burning
accumulate and become widespread to a degree significant enough to affect
regional climate.
A
three-kilometer (1.9-mile)-thick brown cloud has been linked to altered
rainfall patterns in
Because
of the large-scale dimming by ABCs, they have a mitigating effect on the
warming of the ocean in the region that's also associated with greenhouse
gas-driven climate changes.
"We're
showing that pollution from human activities as simple as burning wood or
driving a vehicle with a diesel engine can change these massive atmospheric
phenomena in a significant way," said the paper's lead author, Amato Evan
of the
"This
underscores the importance of getting a handle on emissions in the
region."
Historically,
the onset of the monsoon season in summer months has produced strong winds in
the lower and upper atmosphere that travel in opposite directions, also known
as vertical wind shear, which makes formation of cyclones virtually impossible
in July and August.
Thus
despite warm sea surface temperatures, the
But
the scientists found a trend of increasingly strong cyclones in the months
immediately preceding monsoon season.
A
1998 cyclone that made landfall in
Gonu produced category 5-strength winds in excess
of 250 kilometers per hour (156 miles per hour). Phet
was a category 4 storm.
"This
study is a striking example of how human actions, on a large enough scale--in
this case, massive regional air pollution caused by inefficient fuel
combustion--can result in unintended consequences," said Anjuli Bamzai, program director
in the National Science Foundation's Division of Atmospheric and Geospace Sciences, which funded the research.
"These
consequences include highly destructive summer cyclones that were rare or
non-existent in this monsoon region 30 or so years ago."
The
scientists used findings from direct observations and model studies of ABCs
made by Scripps Institution of Oceanography climate and atmospheric scientist Veerabhadran Ramanathan, a paper
co-author.
Among
the findings is that brown clouds inhibited summertime warming of the surface,
which caused sea surface temperatures in the northern
The
team modeled the effects of brown clouds on atmospheric and oceanic circulation
patterns.
They
found that ABCs changed the circulation of the atmosphere and reduced the climatological vertical wind shear.
"This
study adds a major dimension to a long list of negative effects that brown
clouds have, including rainfall reduction, Himalayan glacial melting,
significant crop damages and deaths of a million or more people
annually," said Ramanathan.
"The
one silver lining is that the atmospheric concentrations of these pollutants
can be reduced drastically and quickly using available technologies."
Those
technologies include, says Ramanathan, diesel filters
for trucks and buses; two-stroke engines running on LPG fuel; energy-efficient
and less polluting cookstoves; and less polluting
brick-kilns.
The
other co-authors of the study are James P. Kossin of
the
The
NOAA Climate Program Office provided additional support for the study.
-NSF-