NASA Satellites Illuminate Pollution's Influence on Clouds, Climate

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Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
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Lynn Chandler 301-286-2806
NASA Goddard Space Flight Center, Greenbelt, Md.
lynn.chandler-1@nasa.gov

NEWS RELEASE: 2008-085 May 27, 2008

NASA Satellites Illuminate Pollution's Influence on Clouds, Climate

PASADENA, Calif. -- Using data from instruments in a constellation of NASA satellites,
scientists have discovered that they can see deep inside of clouds. The satellites are taking first-
of-a-kind measurements, shedding new light on the link between clouds, pollution and rainfall.

Jonathan Jiang of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and colleagues used
sensors from multiple satellites in the Afternoon Constellation, more commonly called the A-
Train, to find that South American clouds infused with airborne pollution -- classified as
"polluted clouds" -- tend to produce less rain than their "clean" counterparts during the region's
dry season. Details of the findings are presented today at the American Geophysical Union's 2008
Joint Assembly in Fort Lauderdale, Fla.

"The A-Train is providing a new way to examine cloud types," said Mark Schoeberl, A-Train
project scientist at NASA's Goddard Space Flight Center, Greenbelt, Md.

Discovery of the link between rain and pollution was possible due to near-simultaneous
measurements from the A-Train satellites. "Typically, it is very hard to get a sense of how
important the effect of pollution on clouds is," said Anne Douglass, deputy project scientist at
Goddard for NASA's Aura satellite. "With the A-Train, we can see the clouds every day and
we're getting confirmation on a global scale that we have an issue here."

Jiang's team used the JPL-developed and managed Microwave Limb Sounder on the A-Train's
Aura satellite to measure the level of carbon monoxide in clouds. The presence of carbon
monoxide implies the presence of smoke and other aerosols, which usually come from the same
emission source, such a power plant or agricultural fire.

With the ability to distinguish between polluted and clean clouds, the team next used Aqua's
Moderate Resolution Imaging Spectroradiometer to study how ice particle sizes change when
aerosol pollution is present in the clouds. The team also used NASA's Tropical Rainfall
Measuring Mission satellite to measure the amount of precipitation falling from the polluted and
clean clouds. All three measurements together show the relationship between pollution, clouds
and precipitation.

The team found that polluted clouds suppressed rainfall during the June-to-October dry season in
South America, which is also a period of increased agricultural burning. During that period it was
more difficult for the measurably smaller ice particles in aerosol-polluted clouds to grow large
enough to fall as rain.

This trend turned up seasonal and regional differences, however, and aerosol pollution was
found, on average, to be less of a factor during the wet monsoon seasons in South America and in
South Asia. Other physical effects, such as large-scale dynamics and rainy conditions that clear
the air of aerosol particles, might also be at play, the researchers suggest.

"The complexity of interactions between aerosols and clouds poses difficult problems that no one
satellite instrument can solve," said Jiang. "But when you put parameters from multiple satellites
all together, you will find much more information than from a single instrument alone."

The five satellites of the A-Train -- NASA's Aqua, Aura, CloudSat, Cloud-Aerosol Lidar and
Infrared Pathfinder Satellite Observation (Calipso) and the French Space Agency's Polarization
and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a
Lidar, or Parasol -- orbit only eight minutes apart and can be thought of as an extended satellite
observatory, providing unprecedented information about clouds, aerosols and atmospheric
composition.

For information about NASA and agency programs, visit: http://www.nasa.gov/home . For
information about the Microwave Limb Sounder on Aura, visit: http://mls.jpl.nasa.gov/ .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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