This artist's concept shows how the satellites composing the A-Train fly in formation to make near-simultaneous observations of Earth. Image credit: NASA
May 27, 2008
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.
Media contacts: Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov
Lynn Chandler 301-286-2806
NASA Goddard Space Flight Center, Greenbelt, Md.
lynn.chandler-1@nasa.gov
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