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FOR IMMEDIATE RELEASEDecember 8, 1997
SEASAT, NSCAT DETECT CHANGES IN GREENLAND ICE SHEET
Scientists comparing data collected by the Seasat
Scatterometer (SASS) with images acquired by the NASA
Scatterometer (NSCAT) have detected significant changes in the
characteristics and extent of dry snow cover at Greenland's
highest elevations during the 18-year gap between both missions.
Dr. Mark Drinkwater of NASA's Jet Propulsion Laboratory,
Pasadena, CA, and co-author Dr. David Long of Bringham Young
University, Provo, Utah, will be presenting their findings this
week at the annual fall meeting of the American Geophysical Union
in San Francisco, CA. The special session on Greenland will be
held on Monday, Dec. 8, at 10:30 a.m. Pacific Standard Time.
"The area impacted by recent summer melting on Greenland is
significantly larger than that previously observed. It appears
that climate changes over the last two decades have influenced
patterns of snow accumulation and melting on Greenland. A
persistent increase in the melting of the ice sheet would
ultimately affect sea levels," Drinkwater said. "The extent of
the polar ice sheets helps preserve the global energy balance as
the ice sheets reflect incoming solar energy and, thus, help
regulate Earth's temperature."
NASA's Seasat mission was launched in 1978 and carried five
instruments to measure wind speed and direction, sea-surface
temperature, the amount of water in the atmosphere, ocean waves
and the polar ice fields. Seasat operated for 100 days before an
electrical short circuit ended the mission.
The NASA Scatterometer (NSCAT), designed to study wind speed
and direction over the oceans, was launched in August 1996 on
Japan's Advanced Earth Observing Satellite (ADEOS). However, the
satellite suffered a fatal solar array problem that prematurely
ended the mission on June 30, 1997.
Despite the short lifetimes of both missions, the
scatterometers have provided scientists with valuable information
about winds over the ocean. Data from the missions have also been
used to study changes in the polar ice sheets.
"Although originally designed to measure ocean winds,
spaceborne microwave radar scatterometers such as NSCAT can be
used effectively to study changes in large polar ice sheets. Our
results show a clear reduction in the location and extent of the
dry-snow zone as a result of increased melting since 1978. The
largest changes occur at the boundary of the dry snow zone in the
southwestern part of the ice sheet. The dry-snow zone is the high
altitude portion of the Greenland ice cap, which normally
experiences no summer melting," Drinkwater said. "These changes
are consistent with a 10-year warming trend and an increase of
more than 1 degree C (1.8 degrees F) between 1979 and the
present day, except for the summer of 1992, when ash from the Mt.
Pinatubo eruption may have temporarily helped to cool the
Scientists need a long-term, consistent measurement record
to help them determine the extent of melting and the impact of
climate change upon the Greenland and Antarctic ice sheets. NASA
has approved the Quick Scatterometer mission (QuikSCAT) to fill
in the measurement gap caused by the loss of NSCAT. These data
will help scientists continue to monitor the changes on Greenland
and around the globe.
The NSCAT and Seasat images are available on JPL's web site
JPL, a division of the California Institute of Technology,
managed the Seasat and NSCAT missions for NASA's Office of
Mission to Planet Earth, Washington, DC.