Jul 24 2012

From The Space Library

RELEASE: 12-249 SATELLITES SEE UNPRECEDENTED GREENLAND ICE SHEET SURFACE MELT

WASHINGTON -- 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 2-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. 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." 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.

RELEASE: 12-255 NASA MARS ORBITER REPOSITIONED TO PHONE HOME MARS LANDING

PASADENA, Calif. -- NASA's Mars Odyssey spacecraft has successfully adjusted its orbital location to be in a better position to provide prompt confirmation of the August landing of the Curiosity rover. The Mars Science Laboratory (MSL) spacecraft carrying Curiosity can send limited information directly to Earth as it enters Mars' atmosphere. Before the landing, Earth will set below the Martian horizon from the descending spacecraft's perspective, ending that direct route of communication. Odyssey will help to speed up the indirect communication process. NASA reported during a July 16 news conference that Odyssey, which originally was planned to provide a near-real-time communication link with Curiosity, had entered safe mode July 11. This situation would have affected communication operations, but not the rover's landing. Without a repositioning maneuver, Odyssey would have arrived over the landing area about two minutes after Curiosity landed. A spacecraft thruster burn Tuesday lasting about six seconds has nudged Odyssey about six minutes ahead in its orbit. Odyssey now is operating normally, and confirmation of Curiosity's landing is expected to reach Earth at about 10:31 p.m. PDT Aug. 5, as originally planned. "Information we are receiving indicates the maneuver has been completed as planned," said Gaylon McSmith, Mars Odyssey project manager at NASA's Jet Propulsion Laboratory (JPL), in Pasadena, Calif. "Odyssey has been working at Mars longer than any other spacecraft, so it is appropriate that it has a special role in supporting the newest arrival." Two other Mars orbiters, NASA's Mars Reconnaissance Orbiter (MRO) and the European Space Agency's Mars Express, also will be in position to receive radio transmissions from MSL during its descent. However, they will be recording information for later playback. Only Odyssey can relay information immediately. Odyssey arrived at Mars in 2001. In addition to its own scientific observations, it has served as a communications relay for NASA's Spirit and Opportunity Mars rovers and the Phoenix lander. Spirit and Phoenix are no longer operational. Odyssey and MRO will provide communication relays for Curiosity during the rover's two-year prime mission. Odyssey and MSL, with its Curiosity rover, are managed by JPL for NASA's Science Mission Directorate in Washington. Curiosity was designed, developed and assembled at JPL. The Odyssey spacecraft is operated by JPL and Lockheed Martin in Denver. Lockheed Martin Space Systems in Denver built Odyssey.