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Frontiers
Climate Modelers Have ACCE in the Hole
September/October 1998
Bobbing in
the Atlantic Ocean are hundreds of floats that may make it possible to
predict global climate patterns decades in advance. The floats are part
of the NSF-supported Atlantic Circulation and Climate Experiment (ACCE).
Climate is an ever-changing dance performed
by two huge systems, the atmosphere and the ocean. Interactions
between the systems are key to anticipating longer-period climate
changes.
Since 1997, researchers have tossed overboard
hundreds of data-gathering floats. The floats sink to a preset
depth of 1,000 meters (the bottom of the ocean layer most in
contact with the atmosphere). After 10 days, they ascend. On
the way up, they measure such water properties as temperature
and salinity. At the surface, the floats send information to
a satellite, enabling scientists to track where this layer of
ocean has traveled and the amount of heat and salt it carried.
ACCE researcher Russ Davis of Scripps Institution
of Oceanography and Breck Owens of Woods Hole Oceanographic Institute
have deployed about 150 floats in the subpolar gyre (or vortex)
of the North Atlantic. Among their findings: an unexpected direct
path by which Labrador Sea Water enters the subpolar gyre. The
floats are efficient and reliable despite the harsh environment,
says Davis. "This means they are ready for routine and
widespread use in a global observing system."
Climate modelers are using this information
to constrain and improve their models in real time. "It's
thrilling," says ACCE team member James Carton, a University
of Maryland oceanographer. "Meteorologists have been playing
this game for a long time, but the oceanographers have had so
little data and so little confidence in their models that we've
hesitated to make long-term predictions."
According to Eric Itsweire, associate program
director of NSF's Physical Oceanography Program, this work
has generated excitement throughout the field. Some might even
think of the new experience as the oceanographic equivalent of
floating on air.
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