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   Satellites See Unprecedented Greenland Ice Sheet Surface Melt    
      
   July 24, 2012: For several days this month, Greenland's surface ice cover   
   melted over a larger area than at any time in more than 30 years of satellite   
   observations. Nearly the entire ice cover of Greenland, from its thin,   
   low-lying coastal edges to its two-mile-thick center, experienced some degree   
   of melting at its surface, according to measurements from three independent   
   satellites analyzed by NASA and university scientists.   
      
   On average in the summer, about half of the surface of Greenland's ice sheet   
   naturally melts. At high elevations, most of that melt water quickly refreezes   
   in place. Near the coast, some of the melt water is retained by the ice sheet   
   and the rest is lost to the ocean. But this year the extent of ice melting at   
   or near the surface jumped dramatically. According to satellite data, an   
   estimated 97 percent of the ice sheet surface thawed at some point in   
   mid-July.    
      
   http://science.nasa.gov/media/medialibrary/2012/07/24/icemap.jpg   
      
   Extent of surface melt over Greenland's ice sheet on July 8 (left) and July 12   
   (right). Measurements from three satellites showed that on July 8, about 40   
   percent of the ice sheet had undergone thawing at or near the surface. In just   
   a few days, the melting had dramatically accelerated and an estimated 97   
   percent of the ice sheet surface had thawed by July 12.    
   Researchers have not yet determined whether this extensive melt event will   
   affect the overall volume of ice loss this summer and contribute to sea level   
   rise.   
      
   "The Greenland ice sheet is a vast area with a varied history of change. This   
   event, combined with other natural but uncommon phenomena, such as the large   
   calving event last week on Petermann Glacier, are part of a complex story,"   
   said Tom Wagner, NASA's cryosphere program manager in Washington. "Satellite   
   observations are helping us understand how events like these may relate to one   
   another as well as to the broader climate system."   
      
   Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena, Calif., was   
   analyzing radar data from the Indian Space Research Organisation's (ISRO)   
   Oceansat-2 satellite last week when he noticed that most of Greenland appeared   
   to have undergone surface melting on July 12. Nghiem said, "This was so   
   extraordinary that at first I questioned the result: was this real or was it   
   due to a data error?"   
      
   Nghiem consulted with Dorothy Hall at NASA's Goddard Space Flight Center in   
   Greenbelt, Md. Hall studies the surface temperature of Greenland using the   
   Moderate-resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua   
   satellites. She confirmed that MODIS showed unusually high temperatures and   
   that melt was extensive over the ice sheet surface.   
      
   Thomas Mote, a climatologist at the University of Georgia, Athens, Ga; and   
   Marco Tedesco of City University of New York also confirmed the melt seen by   
   Oceansat-2 and MODIS with passive-microwave satellite data from the Special   
   Sensor Microwave Imager/Sounder on a U.S. Air Force meteorological satellite.   
      
   The melting spread quickly. Melt maps derived from the three satellites showed   
   that on July 8, about 40 percent of the ice sheet's surface had melted. By   
   July 12, 97 percent had melted.   
      
   This extreme melt event coincided with an unusually strong ridge of warm air,   
   or a heat dome, over Greenland. The ridge was one of a series that has   
   dominated Greenland's weather since the end of May. "Each successive ridge has   
   been stronger than the previous one," said Mote. This latest heat dome started   
   to move over Greenland on July 8, and then parked itself over the ice sheet   
   about three days later. By July 16, it had begun to dissipate.   
      
   Even the area around Summit Station in central Greenland, which at 2 miles   
   above sea level is near the highest point of the ice sheet, showed signs of   
   melting. Such pronounced melting at Summit and across the ice sheet has not   
   occurred since 1889, according to ice cores analyzed by Kaitlin Keegan at   
   Dartmouth College in Hanover, N.H. A National Oceanic and Atmospheric   
   Administration weather station at Summit confirmed air temperatures hovered   
   above or within a degree of freezing for several hours July 11-12.   
      
   "Ice cores from Summit show that melting events of this type occur about once   
   every 150 years on average. With the last one happening in 1889, this event is   
   right on time," says Lora Koenig, a Goddard glaciologist and a member of the   
   research team analyzing the satellite data. "But if we continue to observe   
   melting events like this in upcoming years, it will be worrisome."    
      
      
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
      
   More Information    
   Nghiem's finding while analyzing Oceansat-2 data was the kind of benefit that   
   NASA and ISRO had hoped to stimulate when they signed an agreement in March   
   2012 to cooperate on Oceansat-2 by sharing data.     
      
      
   Regards,   
      
   Roger    
   --- timEd/386 1.10.y2k+   
    * Origin: NCS BBS - Houma, LA - (1:3828/7)