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January
31, 2007
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NASA SPACE SLEUTH HUNTS THE TRAIL OF
EARTH'S WATER
For the first time, NASA scientists
have used a shrewd
spaceborne detective to track the origin and movement of water vapor
throughout
Earth's atmosphere. This perspective is vital to improve the
understanding of
Earth's water cycle and its role in weather and climate.
NASA's newest detective in the mysteries of atmospheric water vapor is
the
Tropospheric Emission Spectrometer instrument on the Aura satellite. A
team of
scientists from NASA's Jet Propulsion Laboratory, Pasadena,
Calif., and the University
of Colorado,
Boulder,
used the instrument's observations
of heavy and light water vapor to retrace the "history" of water over
oceans and continents, from ice and liquid to vapor and back again.
Heavy water
vapor molecules have more neutrons than lighter ones do.
By analyzing the distribution of the heavy and light molecules, the
team was
able to deduce the sources and processes that cycle water vapor, the
most
abundant greenhouse gas in Earth's atmosphere.
The team found that tropical rainfall evaporation and water "exhaled"
by forests are key sources of moisture in the tropical atmosphere. They
noted
that more water than they had expected is transported over land rather
than
ocean into the lower troposphere (Earth's lowermost atmosphere),
especially
over the Amazon
River basin
and tropical Africa.
"One might expect most of the water to come directly from the wet
ocean," said study co-author Dr. David Noone of the University
of Colorado.
"Instead, it appears that thunderstorm activity over the tropical
continents plays a key role in keeping the troposphere hydrated."
The team found that in the tropics and regions of tropical rain clouds,
rainfall evaporation significantly adds moisture to the lower
troposphere, with
typically 20 percent and up to 50 percent of rain there evaporating
before it
reaches the ground. The atmosphere retains this water, which can be
used to
make clouds. The strength and location of this evaporation give
scientists new
insight into how water in Earth's atmosphere helps move energy from
Earth's
surface upwards. The main role of the atmosphere in Earth's climate
system is
to take energy deposited by the sun and dispose of it back into space.
The team also found evidence that water transported upwards by
thunderstorm
activity over land originates from both plant "exhalation" in large
forests and evaporation over nearby oceans. The balance between these
two
different sources tells us how vegetation interacts with climate and
helps
maintain regional rainfall levels.
"This link between vegetation, hydrology and climate has implications
for
how societies choose to manage their ecological resources," said Noone.
"Our measurements provide a baseline against which future changes in
vegetation-climate interactions can be measured."
The details of this journey are critical for understanding clouds and
climate,
as well as changes in precipitation patterns and water resources, Noone
explained. "Our study measures the conditions under which precipitation
and evaporation occur, providing insights into the processes
responsible.
Better knowledge of these processes ultimately leads to a clearer
understanding
of the factors that drive the global water cycle and its importance in
climate
and global climate change."
Noone and his co-authors said there has been a general lack of
information on
the way water moves around in Earth's atmosphere – where it
comes from and
where it ends up.
"Since we measure the history of water, so to speak, we can tell the
difference between air masses that have undergone extensive
condensation from
those that are more dominated by evaporation from the ocean surface,"
said
study co-author Dr. John Worden of JPL.
"These results also lay the groundwork for research to help interpret
the
isotopic measurements that scientists use to study Earth's climate in
the
past," added JPL co-author Dr. Kevin Bowman.
Study results appear in the February 1 issue of the journal Nature.
For
more information and images,
visit:
http://www.jpl.nasa.gov/news/news.cfm?release=2007-009
For
more information about the Tropospheric Emission
Spectrometer, visit: http://www.nasa.gov/aura
and http://tes.jpl.nasa.gov/
##
Contact:
Alan Buis
NASA Jet Propulsion Laboratory
818-354-0474
alan.d.buis@jpl.nasa.gov
This text is
derived from:
http://www.jpl.nasa.gov/news/news.cfm?release=2007-009
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