gpc
17-02-2006, 20:47
Posto due notizie dalla newsletter della Nasa, una vecchiotta e una di un paio di giorni fa.
http://www.kintera.org/atf/cf/%7B127BCCB8-B18B-48EC-86CC-B465A792975E%7D/NASA-NEWS-600-1172.GIF
Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
News Release: 2005-176 December 20, 2005
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 Tapley.
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:
http://www.nasa.gov/vision/earth/lookingatearth/grace-images-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) 2203/601-3068.
JPL is managed for NASA by the California Institute of Technology in Pasadena.
-end-
News Release: 2006-023 February 16, 2006
GreenlandIce Loss Doubles in Past Decade, Raising Sea Level Faster
The loss of ice from Greenland doubled between 1996 and 2005, as its glaciers flowed faster into the ocean in response to a generally warmer climate, according to a NASA/University of Kansas study.
The study will be published tomorrow in the journal Science. It concludes the changes to Greenland's glaciers in the past decade are widespread, large and sustained over time. They are progressively affecting the entire ice sheet and increasing its contribution to global sea level rise.
Researchers Eric Rignot of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Pannir Kanagaratnam of the University of Kansas Center for Remote Sensing of Ice Sheets, Lawrence, used data from Canadian and European satellites. They conducted a nearly comprehensive survey of Greenland glacial ice discharge rates at different times during the past 10 years.
"The Greenland ice sheet's contribution to sea level is an issue of considerable societal and scientific importance," Rignot said. "These findings call into question predictions of the future of Greenland in a warmer climate from computer models that do not include variations in glacier flow as a component of change. Actual changes will likely be much larger than predicted by these models."
The evolution of Greenland's ice sheet is being driven by several factors. These include accumulation of snow in its interior, which adds mass and lowers sea level; melting of ice along its edges, which decreases mass and raises sea level; and the flow of ice into the sea from outlet glaciers along its edges, which also decreases mass and raises sea level. This study focuses on the least well known component of change, which is glacial ice flow. Its results are combined with estimates of changes in snow accumulation and ice melt from an independent study to determine the total change in mass of the Greenland ice sheet.
Rignot said this study offers a comprehensive assessment of the role of enhanced glacier flow, whereas prior studies of this nature had significant coverage gaps. Estimates of mass loss from areas without coverage relied upon models that assumed no change in ice flow rates over time. The researchers theorized if glacier acceleration is an important factor in the evolution of the Greenland ice sheet, its contribution to sea level rise was being underestimated.
To test this theory, the scientists measured ice velocity with interferometric synthetic-aperture radar data collected by the European Space Agency's Earth Remote Sensing Satellites 1 and 2 in 1996; the Canadian Space Agency's Radarsat-1 in 2000 and 2005; and the European Space Agency's Envisat Advanced Synthetic Aperture Radar in 2005. They combined the ice velocity data with ice sheet thickness data from airborne measurements made between 1997 and 2005, covering almost Greenland's entire coast, to calculate the volumes of ice transported to the ocean by glaciers and how these volumes changed over time. The glaciers surveyed by those satellite and airborne instrument data drain a sector encompassing nearly 1.2 million square kilometers (463,000 square miles), or 75 percent of the Greenland ice sheet total area.
From 1996 to 2000, widespread glacial acceleration was found at latitudes below 66 degrees north. This acceleration extended to 70 degrees north by 2005. The researchers estimated the ice mass loss resulting from enhanced glacier flow increased from 63 cubic kilometers in 1996 to 162 cubic kilometers in 2005. Combined with the increase in ice melt and in snow accumulation over that same time period, they determined the total ice loss from the ice sheet increased from 96 cubic kilometers in 1996 to 220 cubic kilometers in 2005. To put this into perspective, a cubic kilometer is one trillion liters (approximately 264 billion gallons of water), about a quarter more than Los Angeles uses in one year.
Glacier acceleration has been the dominant mode of mass loss of the ice sheet in the last decade. From 1996 to 2000, the largest acceleration and mass loss came from southeast Greenland. From 2000 to 2005, the trend extended to include central east and west Greenland.
"In the future, as warming around Greenland progresses further north, we expect additional losses from northwest Greenland glaciers, which will then increase Greenland's contribution to sea level rise," Rignot said.
For information about NASA and agency programs on the Web, visit:
http://www.nasa.gov/home .
For University of Kansas Center for Remote Sensing of Ice Sheets information, visit:
http://www.cresis.ku.edu/flashindex.htm .
JPL is managed for NASA by the California Institute of Technology in Pasadena.
-end-
http://www.kintera.org/atf/cf/%7B127BCCB8-B18B-48EC-86CC-B465A792975E%7D/NASA-NEWS-600-1172.GIF
Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
News Release: 2005-176 December 20, 2005
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 Tapley.
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:
http://www.nasa.gov/vision/earth/lookingatearth/grace-images-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) 2203/601-3068.
JPL is managed for NASA by the California Institute of Technology in Pasadena.
-end-
News Release: 2006-023 February 16, 2006
GreenlandIce Loss Doubles in Past Decade, Raising Sea Level Faster
The loss of ice from Greenland doubled between 1996 and 2005, as its glaciers flowed faster into the ocean in response to a generally warmer climate, according to a NASA/University of Kansas study.
The study will be published tomorrow in the journal Science. It concludes the changes to Greenland's glaciers in the past decade are widespread, large and sustained over time. They are progressively affecting the entire ice sheet and increasing its contribution to global sea level rise.
Researchers Eric Rignot of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Pannir Kanagaratnam of the University of Kansas Center for Remote Sensing of Ice Sheets, Lawrence, used data from Canadian and European satellites. They conducted a nearly comprehensive survey of Greenland glacial ice discharge rates at different times during the past 10 years.
"The Greenland ice sheet's contribution to sea level is an issue of considerable societal and scientific importance," Rignot said. "These findings call into question predictions of the future of Greenland in a warmer climate from computer models that do not include variations in glacier flow as a component of change. Actual changes will likely be much larger than predicted by these models."
The evolution of Greenland's ice sheet is being driven by several factors. These include accumulation of snow in its interior, which adds mass and lowers sea level; melting of ice along its edges, which decreases mass and raises sea level; and the flow of ice into the sea from outlet glaciers along its edges, which also decreases mass and raises sea level. This study focuses on the least well known component of change, which is glacial ice flow. Its results are combined with estimates of changes in snow accumulation and ice melt from an independent study to determine the total change in mass of the Greenland ice sheet.
Rignot said this study offers a comprehensive assessment of the role of enhanced glacier flow, whereas prior studies of this nature had significant coverage gaps. Estimates of mass loss from areas without coverage relied upon models that assumed no change in ice flow rates over time. The researchers theorized if glacier acceleration is an important factor in the evolution of the Greenland ice sheet, its contribution to sea level rise was being underestimated.
To test this theory, the scientists measured ice velocity with interferometric synthetic-aperture radar data collected by the European Space Agency's Earth Remote Sensing Satellites 1 and 2 in 1996; the Canadian Space Agency's Radarsat-1 in 2000 and 2005; and the European Space Agency's Envisat Advanced Synthetic Aperture Radar in 2005. They combined the ice velocity data with ice sheet thickness data from airborne measurements made between 1997 and 2005, covering almost Greenland's entire coast, to calculate the volumes of ice transported to the ocean by glaciers and how these volumes changed over time. The glaciers surveyed by those satellite and airborne instrument data drain a sector encompassing nearly 1.2 million square kilometers (463,000 square miles), or 75 percent of the Greenland ice sheet total area.
From 1996 to 2000, widespread glacial acceleration was found at latitudes below 66 degrees north. This acceleration extended to 70 degrees north by 2005. The researchers estimated the ice mass loss resulting from enhanced glacier flow increased from 63 cubic kilometers in 1996 to 162 cubic kilometers in 2005. Combined with the increase in ice melt and in snow accumulation over that same time period, they determined the total ice loss from the ice sheet increased from 96 cubic kilometers in 1996 to 220 cubic kilometers in 2005. To put this into perspective, a cubic kilometer is one trillion liters (approximately 264 billion gallons of water), about a quarter more than Los Angeles uses in one year.
Glacier acceleration has been the dominant mode of mass loss of the ice sheet in the last decade. From 1996 to 2000, the largest acceleration and mass loss came from southeast Greenland. From 2000 to 2005, the trend extended to include central east and west Greenland.
"In the future, as warming around Greenland progresses further north, we expect additional losses from northwest Greenland glaciers, which will then increase Greenland's contribution to sea level rise," Rignot said.
For information about NASA and agency programs on the Web, visit:
http://www.nasa.gov/home .
For University of Kansas Center for Remote Sensing of Ice Sheets information, visit:
http://www.cresis.ku.edu/flashindex.htm .
JPL is managed for NASA by the California Institute of Technology in Pasadena.
-end-