HR: 1330h
AN: OS32D-146 [PDF]
TI: An Idealized Model of the Seasonal Variability in the Alaska Coastal Current
AU: * Williams, W J
EM: wjw@ims.uaf.edu
AF: Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK 99775-7220
United States
AU: Weingartner, T J
EM: weingart@ims.uaf.edu
AF: Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK 99775-7220
United States
AB:
The Alaska Coastal Current (ACC) is a wind and
buoyancy forced, 30-50 km-wide current of
low-salinity water that flows along the coast of
the Gulf of Alaska from southeastern Alaska to
Unimak Pass where it enters the Bering Sea. It is
a consequence of the massive coastal freshwater
discharge which is distributed in numerous small
rivers draining from coastal mountain
ranges. Seasonally, the discharge is a minimum in
winter and increases through the summer to a
maximum in fall. Annually, it accounts for nearly
40\% of the freshwater flux into the Gulf of
Alaska. The ACC can either store this freshwater,
mix it offshore, or transport it to the Bering
Sea.
The wind-stress along the coast of the Gulf of
Alaska is generally cyclonic due to the Aleutian
Low. It is strong and persistent in winter and
weak and more variable in summer. The ACC is
unique among coastal currents because of the
downwelling wind stress, the massive, distributed
coastal buoyancy forcing and the relatively-deep,
nearshore bottom depths.
CTD sections across the ACC show the current to be
narrow, deep and bottom-attached in winter; but
wider, shallow and predominantly surface-trapped
in summer. We use the Regional Ocean Modeling
System (ROMS) forced by a combination of
downwelling wind-stress and a half-line source
coastal-buoyancy-influx as a simplified model
of the ACC to examine the dynamical processes that govern the
seasonal cycle. The origins of the ACC
are represented by the beginning of the line
source. For this model, the scales of time
evolution, the dynamical balance and density
balance, and the relative importance of
cross-shelf mixing to along-shelf transport of
freshwater are presented. The numerical
simulations of the half-line source show a
narrow deep `ACC' during winter forcing and a
wider, shallow `ACC' during summer forcing.
DE: 4219 Continental shelf processes
DE: 4227 Diurnal, seasonal, and annual cycles
DE: 4255 Numerical modeling
DE: 4508 Coriolis effects
DE: 4512 Currents
SC: OS
MN: 2002 Ocean Sciences Meeting