Hi My Friends: A VUELO DE UN QUINDE EL BLOG., 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
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. In the image, the areas
classified as “probable melt” (light pink) correspond to those sites
where at least one satellite detected surface melting. The areas
classified as “melt” (dark pink) correspond to sites where two or three
satellites detected surface melting. The satellites are measuring
different physical properties at different scales and are passing over
Greenland at different times. As a whole, they provide a picture of an
extreme melt event about which scientists are very confident. Credit:
Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth
Observatory
› Hi-res of left image
› Hi-res of right image
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.
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.
Maria-José Viñas
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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