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Analysis of Arctic Sea Ice Anomalies in a Coupled Model
Control Simulation
Richard I. Cullather
Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, USA
L.-Bruno Tremblay
Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, Canada
In a 600-year control run simulation of the Community Climate System Model,
version 3 (CCSM3) of the National Center for Atmospheric Research, three events
of extraordinary minimum September sea ice extent are identified, from which the
system recovers within a few years. The control simulation is run in a stable climate
mode using constant 1990 solar, trace gas, and aerosol forcing. The identified
events are all of similar magnitude to the observed 2007 record low Arctic ice
cover. In the first event (simulation year 451), the record low ice extent coincides
with an extreme, cyclonic phase of atmospheric circulation and follows a 10-year
period of steady decline in Northern Hemisphere sea ice volume that is associated
with increased winter ice export. The ice extent recovered the following year when
both the ice export and summer melt returned to more normal values. However,
Arctic ice volume did not fully recover until 20 years after the event. In the second
event (model year 490), the system was again preconditioned by a 10-year decline
in Arctic sea ice volume because of larger than normal ice export. The event itself
was associated with a coincident peak in early summer melt and ice export. During
the recovery phase, the ice extent again rapidly returned to normal while the sea ice
volume continued to decline for another 10 years, to its lowest value of the entire
simulation. The recovery in Northern Hemisphere sea ice volume is associated
with periods of reduced wintertime ice export through Fram Strait. The third event
(model year 556-558) is characterized by a longer-lived anomaly (3 years). The
system was not preconditioned by low ice volume, indicating that redistribution
of sea ice (rather than ice mass loss) played an important role. Recovery for the
third event is associated with a period of low ice export associated with a rapid
return of an expanded Beaufort Gyre, which serves to recirculate sea ice within
the Arctic Ocean. Notwithstanding known climate model deficiencies, the control
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