For the first time, scientists have demonstrated precise
measurements of Earth’s changing gravity field can
effectively monitor changes in the planet’s climate and
weather.
This finding comes from more than a year’s worth of data from
the Gravity Recovery and Climate Experiment (GRACE). GRACE is
a two-spacecraft, joint partnership of NASA and the German
Aerospace Center.
Results published in the journal Science show monthly changes
in the distribution of water and ice masses could be
estimated by measuring changes in Earth’s gravity field. The
GRACE data measured the weight of up to 10 centimeters (four
inches) of groundwater accumulations from heavy tropical
rains, particularly in the Amazon basin and Southeast Asia.
Smaller signals caused by changes in ocean circulation were
also visible.
Launched in March 2002, GRACE tracks changes in Earth’s
gravity field. GRACE senses minute variations in
gravitational pull from local changes in Earth’s mass. To do
this, GRACE measures, to one-hundredth the width of a human
hair, changes in the separation of two identical spacecraft
in the same orbit approximately 220 kilometers (137 miles)
apart.
GRACE maps these variations from month to month, following
changes imposed by the seasons, weather patterns and short-
term climate change. Understanding how Earth’s mass varies
over time is an important component necessary to study
changes in global sea level, polar ice mass, deep ocean
currents, depletion and recharge of continental aquifers.
GRACE monthly maps are up to 100 times more accurate than
existing ones, substantially improving the accuracy of many
techniques used by oceanographers, hydrologists,
glaciologists, geologists and other scientists to study
phenomena that influence climate.
“Measurements of surface water in large, inaccessible river
basins have been difficult to acquire, while underground
aquifers and deep ocean currents have been nearly impossible
to measure,” said Dr. Byron Tapley, GRACE principal
investigator at the University of Texas Center for Space
Research in Austin, Texas. “GRACE gives us a powerful new
tool to track how water moves from one place to another,
influencing climate and weather. These initial results give
us great confidence GRACE will make critical contributions to
climate research in the coming years,” he added.
“The unparalleled accuracy of the GRACE measurements opens a
number of new scientific perspectives,” said Dr. Christoph
Reigber from the GeoForschungsZentrum Potsdam in Germany.
“Observations of mass variations over the ocean will assist
in interpreting annual signals in long-term sea-level change
that have become an important climate change indicator,”
Reigber said.
Dr. Michael Watkins, GRACE project scientist at NASA’s Jet
Propulsion Laboratory, Pasadena, Calif., said the results
mark the birth of a new field of remote sensing. “Over the
past 20 years, we’ve made primitive measurements of changes
in Earth’s gravity field over scales of thousands of
kilometers, but this is the first time we’ve been able to
demonstrate gravity measurements can be truly useful for
climate monitoring,” he said.
“The GRACE gravity measurements will be combined with water
models to sketch an exceptionally accurate picture of water
distribution around the globe. Together with other NASA
spacecraft, GRACE will help scientists better understand the
global water cycle and its changes,” Watkins added.
The University of Texas Center for Space Research has overall
mission responsibility. German mission elements are the
responsibility of GeoForschungsZentrum Potsdam. Science data
processing, distribution, archiving and product verification
are managed under a cooperative arrangement between JPL, the
University of Texas and GeoForschungsZentrum Potsdam.
For more information about GRACE on the Internet, visit
http://www.csr.utexas.edu/GRACE
http://www.gfz-potsdam.de/GRACE
For information about NASA programs on the Internet, visit:
