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AGU Ocean Sciences Meeting (Feb. 2002) COAST abstracts:


Effects of Topography on Currents During an Upwelling Relaxation Event

Sheila OKeefe, P. M. Kosro, and J. A. Harlan

Upwelling events along the west coast of North America are separated
by relaxation events in which the winds weaken or even reverse
to downwelling-favorable. These events influence alongshore and
cross-shelf transport, including larval dispersal. Upwelling
conditions tend to produce southward and offshore advection,
while downwelling conditions tend to produce northward and onshore
advection.  Eddies and other mesoscale current features modify these
larger-scale advection patterns. A sequence including upwelling,
reversal to downwelling, and return to upwelling occurred in
May 1996 near Cape Blanco, Oregon. Wind measurements indicate
upwelling-favorable conditions through May 16, 1996. On May 17-18,
1996 a storm moved through the area with strong downwelling-favorable
winds. After the storm, winds again were upwelling-favorable. During
this period, a Seasonde coastal-based radar system measured surface
currents in the Cape Blanco area, extending approximately 40km
offshore by 30km alongshore. CTD casts, Seasoar tows, and mooring
data provide subsurface data during this period. These data provide
detailed observations of current behavior throughout the upwelling
event and subsequent wind reversal, including the formation of
an anticyclonic eddy over a topographic high, which reverses to
cyclonic when winds return to upwelling-favorable. These detailed
observations provide an opportunity for analysis of the dynamics
behind formation of an eddy over a topographic high and its impact
on cross-shelf transport.