From: LARRY KLAES (ljk4@msn.com)
Date: Wed Aug 28 2002 - 14:49:25 PDT
----- Original Message -----
From: Mark Hess
Sent: Wednesday, August 28, 2002 1:22 PM
To: News Media list.serv
Subject: ATMOSPHERIC WAVE LINKED TO SEA ICE FLOW NEAR GREENLAND, STUDYFINDS
Krishna Ramanujan August 28, 2002
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-3026)
kramanuj@pop900.gsfc.nasa.gov
Release No: 02-132
ATMOSPHERIC WAVE LINKED TO SEA ICE FLOW NEAR GREENLAND, STUDY FINDS
A NASA researcher finds that the amount of sea ice that moves between
Greenland and Spitsbergen, a group of islands north of Norway, is
dependent upon a "wave" of atmospheric pressure at sea level. By
being able to estimate how much sea ice is exported through this
region, called Fram Strait, scientists may develop further insights
into how the ice impacts global climate.
This export of sea ice helps control the thermohaline circulation, a
deep water ocean conveyor belt that moves warm, salty water poleward
and cold, fresh water toward the equator. The thermohaline
circulation is one of the primary mechanisms that maintains the
global heat balance.
Don Cavalieri, a researcher at NASA's Goddard Space Flight Center in
Greenbelt, Md., discovered a link between the transport of sea ice
through this region and the position or phase of the longest sea
level pressure wave circling the Earth at polar latitudes.
Until now, scientists have had inconsistent results when trying to
identify the mechanism behind this transport of sea ice. The North
Atlantic Oscillation, in particular, was unable to explain the
changes in sea ice transport through Fram Strait.
"The significance of this work is the connection between the phase of the longest atmospheric wave called 'wave 1' in sea level pressure and long-term Arctic Ocean and sea ice variability," said Cavalieri.
Sea level pressure is made up of high and low pressure systems as any
weather map will show. The large-scale semi-permanent highs and lows
define the longest pressure waves which are called planetary waves
because they extend thousands of miles and circle the world. The
longest wave, called wave 1, is made up of one ridge (high pressure)
and one trough (low pressure). It turns out that wave 1 is the
dominant pattern at polar latitudes. Because these planetary waves
are so dominant in wintertime atmospheric circulation their
amplitudes (strength) and phases (position) provide useful
information on large-scale wind patterns and thus on sea ice
transport.
The Icelandic Low is the primary weather system in the North
Atlantic. At times this low pressure system extends northeastward
into the Barents Sea. When this happens a secondary low pressure
system may develop in the Barents Sea region. It is the
counterclockwise circulation around this secondary low pressure
system in the Barents Sea that drives sea ice through the Fram
Strait. Whenever this secondary low pressure system exists, wave 1
shifts eastward and is said to be in its eastward phase, as opposed
to a westward phase.
When wave 1 is in its westward mode, the Icelandic Low is more
intense and localized, no longer extending to the Barents Sea.
Because of the position of the Low relative to the Strait, the winds
are more westerly and less ice is forced southward through Fram
Strait.
Variations in the phase of wave 1 between these two extreme modes
also seem to control the cycle of Arctic Ocean circulation which
reverses from clockwise to counterclockwise (or anticyclonic to
cyclonic, respectively) every 6 or 7 years.
Cavalieri used simulations for the 40 year period (1958-1997) from
two computer models to obtain a record of the volume of sea ice that
moved through Fram Strait. The two models each showed a similar
correlation between the eastward phase of wave 1 and movement of sea
ice through the strait, with the exception of two anomalous years
between 1966 and 1967. When those years were removed, one ice-ocean
model, using monthly surface wind and air temperature data, found
that the wave 1 eastward phase explained 70 percent of Arctic ice
export through Fram Strait, while the other model, which used daily
surface wind and air temperature data, accounted for 60 percent of
the sea ice export.
Cavalieri also used Northern Hemisphere monthly sea level pressure
grids to obtain phase and amplitude information for wave 1.
The paper appeared in a recent issue of Geophysical Research Letters.
The study was funded by NASA's Cryospheric Sciences Research Program.
For more information, please see:
http://www.gsfc.nasa.gov/topstory/20020807seaice.html
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