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May 29, 2007
NASA RESEARCHER FINDS DAYS OF
SNOW
MELTING ON THE RISE IN GREENLAND
In
2006, Greenland
experienced more days of melting snow and at
higher altitudes than average over the past 18 years, according to a
new
NASA-funded project using satellite observations.
Daily
satellite observations have shown snow melting on Greenland’s
ice sheet over an increased number of days. The resulting data help
scientists
understand better the speed of glacier flow, how much water will pour
from the
ice sheet into the surrounding ocean and how much of the
sun’s radiation will
reflect back into the atmosphere.
"We now have the ability to monitor melting snow on
Greenland’s ice sheet
on a daily basis using sensors on satellites measuring the
electromagnetic
signal naturally emitted by the ice sheet," said Marco Tedesco,
research
scientist at the Joint Center for Earth Systems Technology
cooperatively
managed by NASA’s Goddard Space Flight Center, Greenbelt,
Md., and the
University of Maryland at Baltimore County, Baltimore.
"The sensors detected that snowmelt occurred more than 10 days longer
than
the average over certain areas of Greenland in 2006," said Tedesco, who
is
lead author of the study, which appears in the May 29 issue of the
American
Geophysical Union's Eos.
Tedesco applied a new method for detecting melting snow to data from
the
Special Sensor Microwave Imaging radiometer (SSM/I) flying aboard the
Defense
Meteorological Satellite Program spacecraft. The sensor can see through
clouds
and does not require sunlight to make measurements, providing
researchers with
multiple daily observations. Tedesco has updated the results annually
since
1988, which has enabled him to analyze trends in the duration of
snowmelt and
extent over specific areas of Greenland.
To understand why these trends are important to track, Tedesco
explained one of
the consequences of melting snow. "Although wet and dry snow look
similar
at first glance, wet and re-frozen snow absorb more of the
sun’s radiation,
reflecting only 50-60 percent back into the atmosphere. Dry snow, on
the other
hand, reflects about 85 percent of the sun’s radiation," he
said. "In
other words, melting snow absorbs three to four times as much energy as
dry
snow, greatly affecting Earth’s energy budget."
The Earth’s energy budget refers to the balance between
incoming sunlight and
outgoing radiant energy.
Greenland's melting snow can have a major
impact on the vast ice sheet and
on sea level around the world. "The melting snow produces liquid water
that will potentially influence sea levels," said Tedesco. "And some
of the liquid water will drain into the glaciers through cracks and
vertical
passages, called moulins, reaching the bedrock below and lubricating
the ice
sheet."
Previous studies by NASA Goddard researchers Jay Zwally and Waleed
Abdalati
have also observed that the water from summer melting at the ice
sheet's base
can increase how fast the ice moves, causing it to contribute more
rapidly to
sea level than previously thought. This phenomenon, together with
others
recently observed, suggest that the ice might respond more quickly to a
warming
climate.
To estimate the overall impact on Greenland's
snow, Tedesco's study calculated a "melt index," which is the number
of melting days multiplied by the melting area. The 2006 data followed
the
increasing trend from 1988 to 2005. Areas along Greenland’s
western, southeastern and northeastern coast witnessed the largest
number of melt
days in 2006.
"The International Polar Year's focus on this part of the world gives
us
an ideal opportunity to combine research results on snowmelt from
satellites as
well as from climate models to better understand how melting is really
affecting the mass balance of Greenland's ice sheet. We need to link
all of
this data together to get a better view of this complex system."
More
information and images:
http://www.nasa.gov/centers/goddard/news/topstory/2007/snowmelt_greenland.html
SSM/I and the
Defense
Meteorological Satellite Program:
http://www.af.mil/factsheets/factsheet.asp?fsID=94
NASA
and the International Polar Year:
http://www.nasa.gov/mission_pages/IPY/main/index.html
Writer:
Gretchen Cook-Anderson, NASA Goddard Space Flight Center
##
Contact:
Lynn Chandler
NASA Goddard Space Flight Center
301-286-2806
This text is
derived from:
http://www.nasa.gov/centers/goddard/news/topstory/2007/snowmelt_greenland.html
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