Artist concept of Seasat

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 northern hemisphere."

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 at

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.

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