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NASA's Grace Finds Greenland Melting Faster

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  • Mike Neuman
    NASA s Grace Finds Greenland Melting Faster, Sees Sumatra Quake 12/20/05 In the first direct, comprehensive mass survey of the entire Greenland ice sheet,
    Message 1 of 1 , Jan 5, 2006
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      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:
      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-

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


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