Icelandic Weather System Deciphers Changes In Arctic Ice Puzzles
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.”
More information is available at:
http://www.gsfc.nasa.gov/topstory/20011001icepuzzle.html
