NASA's Grace Finds Greenland Melting Faster, 'Sees' Sumatra Quake

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.

News Release: 2005-176 December 20, 2005

NASA's Grace Finds Greenland Melting Faster, 'Sees' Sumatra Quake

In the first direct, comprehensive mass survey of the entire
Greenland ice sheet, scientists using data from the NASA/German
Aerospace Center Gravity Recovery and Climate Experiment (Grace)
have measured a significant decrease in the mass of the Greenland
ice cap. Grace is a satellite mission that measures movement in
Earth's mass.

In an update to findings published in the journal Geophysical
Research Letters, a team led by Dr. Isabella Velicogna of the
University of Colorado, Boulder, found that Greenland's ice
sheet decreased by 162 (plus or minus 22) cubic kilometers a
year between 2002 and 2005. This is higher than all previously
published estimates, and it represents a change of about 0.4
millimeters (.016 inches) per year to global sea level rise.

"Greenland hosts the largest reservoir of freshwater in the
northern hemisphere, and any substantial changes in the mass of
its ice sheet will affect global sea level, ocean circulation
and climate," said Velicogna. "These results demonstrate Grace's
ability to measure monthly mass changes for an entire ice sheet -
a breakthrough in our ability to monitor such changes."

Other recent Grace-related research includes measurements of
seasonal changes in the Antarctic Circumpolar Current, Earth's
strongest ocean current system and a very significant force in
global climate change. The Grace science team borrowed
techniques from meteorologists who use atmospheric pressure to
estimate winds. The team used Grace to estimate seasonal
differences in ocean bottom pressure in order to estimate the
intensity of the deep currents that move dense, cold water away
from the Antarctic. This is the first study of seasonal
variability along the full length of the Antarctic Circumpolar
Current, which links the Atlantic, Pacific and Indian Oceans.

Dr. Victor Zlotnicki, an oceanographer at NASA's Jet Propulsion
Laboratory in Pasadena, Calif., called the technique a first
step in global satellite monitoring of deep ocean circulation,
which moves heat and salt between ocean basins. This exchange of
heat and salt links sea ice, sea surface temperature and other
polar ocean properties with weather and climate-related
phenomena such as El Ninos. Some scientific studies indicate
that deep ocean circulation plays a significant role in global
climate change.

The identical twin Grace satellites track minute changes in
Earth's gravity field resulting from regional changes in Earth's
mass. Masses of ice, air, water and solid Earth can be moved by
weather patterns, seasonal change, climate change and even
tectonic events, such as this past December's Sumatra earthquake.
To track these changes, Grace measures micron-scale changes in
the 220-kilometer (137-mile) separation between the two
satellites, which fly in formation. To limit degradation of
Grace's satellite antennas due to atomic oxygen exposure and
thereby preserve mission life, a series of maneuvers was
performed earlier this month to swap the satellites' relative
positions in orbit.

In a demonstration of the satellites' sensitivity to minute
changes in Earth's mass, the Grace science team reported that
the satellites were able to measure the deformation of the
Earth's crust caused by the December 2004 Sumatra earthquake.
That quake changed Earth's gravity by one part in a billion.

Dr. Byron Tapley, Grace principal investigator at the University
of Texas at Austin, said that the detection of the Sumatra
earthquake gravity signal illustrates Grace's ability to measure
changes on and within Earth's surface. "Grace's measurements
will add a global perspective to studies of large earthquakes
and their impacts," said Tapley.

Grace is managed for NASA by JPL. The University of Texas Center
for Space Research has overall mission responsibility.
GeoForschungsZentrum Potsdam, or GFZ, Potsdam, Germany,
is responsible for German mission elements. Science data
processing, distribution, archiving and product verification
are managed jointly by JPL, the University of Texas and GFZ.

Imagery related to these latest Grace findings may be viewed at:

http://www.nasa.gov/vision/earth/loo...-20051220.html.

For more information on Grace, visit:

http://www.csr.utexas.edu/grace or http://www.gfz-potsdam.de/grace .

Other Grace public affairs contacts include: Margaret Baguio,
University of Texas, (512) 471- 6922; Franz Ossing, GFZ,
49 (331) 288-1040; and Vanadis Weber, German Aerospace Center,
49 (0) 2203/601-3068.

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

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