ICELANDIC
WEATHER SYSTEM HELPS DECIPHER CHANGES IN THE ARCTIC ICE PUZZLE Largely
natural "ups and downs" in a weather system centered near Iceland have
contributed to regional variations and an overall decrease in Arctic sea ice cover
over the last twenty years, according to new NASA research. As
this semi-permanent low-pressure system intensifies and weakens, it affects the
amount of air (generally warm) being brought into the Arctic to the east of the
low and the amount of air (generally cold) being swept out of the Arctic to the
west. These changes in turn affect the amount of ice cover in the respective regions,
adding to the effects of climate warming. Claire
L. Parkinson of NASA's Goddard Space Flight Center in Greenbelt, Md., highlights
the changes in Arctic sea ice and their possible connection to the Icelandic low-pressure
system in a paper appearing in the most recent issue of Polar Geography. Parkinson
plotted the extent of sea ice using satellite passive-microwave data from 1979
through 1999. Data were analyzed from the Nimbus 7 satellite and three satellites
of the Defense Meteorological Satellite Program (DMSP). Results confirm an overall
decline in Arctic ice extent that has been connected with climate warming, but
also show regional differences that suggest there are other influences. The
"Icelandic Low" is a key to bringing a greater or lesser amount of warm
air into the Arctic depending on the intensity of the system, and is part of a
larger weather pattern called the North Atlantic Oscillation (NAO). NAO is the
name for changes in the difference of air pressure between the semi- permanent
low-pressure system centered near Iceland (the Icelandic Low) and a semi-permanent
high-pressure system centered near the Azores Islands (better known as the Bermuda-Azores
High). On
average, both of these systems are present all year; however, both are strongest
in winter. When both the high and the low intensify and fluctuate in pressure
relative to one another, they change the circulation of cold and warm air in the
region. When
the Icelandic Low is strong, it forces cold Arctic air southward to the area west
of Iceland and Greenland, setting the stage for increasing sea ice cover in Baffin
Bay, the Labrador Sea, Hudson Bay and the Gulf of St. Lawrence. At the same time,
to the east, warm air that is swept northward reduces ice extent. This warmer
air contributes to the reduced ice extents east and north of Greenland, and the
reduced extent of ice in the entire Arctic overall. "When the Icelandic Low
is weak, it will still bring warm air northward to the east of Iceland, but not
as much as when the Icelandic Low is strong," Parkinson said. The
study examined the ice in nine regions of Northern Hemisphere sea ice cover: the
Arctic Ocean, the Kara and Barents Seas, the Greenland Sea, Baffin Bay/Labrador
Sea, the Gulf of St. Lawrence, Hudson Bay, the Bering Sea, the Canadian Archipelago,
and the Seas of Okhotsk and Japan. The
strength of the Icelandic Low tended to increase from 1979 to 1990, then decrease
in the 1990s. From 1979 to 1990 the ice cover to the east and north of the Low,
in the Kara and Barents Seas and the Arctic Ocean, decreased, while the ice cover
to the west of the Low, in Baffin Bay/Labrador Sea, Hudson Bay and the Gulf of
St. Lawrence, increased. >From
1990 to 1999 the situation was reversed, with the ice cover to the east and north
of the Low increasing and the ice cover to the west of the Low decreasing. "This
regional pattern of reversals in the ice extent trends is highly suggestive of
an Icelandic Low impact, or, more broadly, of an impact from the North Atlantic
Oscillation," Parkinson explained. "Still, the satellite data reveal
an overall decrease in Arctic sea ice extent since 1978." The
overall decrease in sea ice cover has generated questions about whether Arctic
sea ice is being influenced by global warming. Parkinson urges caution in drawing
conclusions for decreases in Arctic ice. "The trend of decreasing ice extent
showed some signs of reversing in the 1990s," she noted. "Whether the
ice cover as a whole will continue to exhibit the decreases that it experienced
over the 1979 to 1999 period might depend on the strength and phase of the NAO,
as well as on long-term trends in the climate system." Back
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