NASA's Grace Finds Greenland Melting Faster
- 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
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:
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-
JPL is managed for NASA by the California Institute of Technology in