Bm. Hickey et al., THE COLUMBIA RIVER PLUME STUDY - SUBTIDAL VARIABILITY IN THE VELOCITYAND SALINITY FIELDS, J GEO RES-O, 103(C5), 1998, pp. 10339-10368
A comprehensive study of the strongly wind driven midlatitude buoyant
plume from the Columbia River, located on the U.S. west coast, demonst
rates that the plume has two basic structures during the fall/winter s
eason, namely, a thin (similar to 5-15 m), strongly stratified plume t
ending west to northwestward during periods of southward or light nort
hward wind stress and a thicker (similar to 10-40 m), weakly stratifie
d plume tending northward and hugging the coast during periods of stro
nger northward stress. The plume and its velocity field respond nearly
instantaneously to changes in wind speed or direction, and the wind f
luctuations have timescales of 2-10 days. Frictional wind-driven curre
nts cause the primarily unidirectional flow down the plume axis to vee
r to the right or left of the axis for northward or southward winds, r
espectively. Farther downstream, currents turn to parallel rather than
cross salinity contours, consistent with a geostrophic balance. In pa
rticular, during periods when the plume is separated from the coast, c
urrents tend to flow around the mound of fresher water. At distances e
xceeding about 20 km from the river mouth, the along-shelf depth-avera
ged flow over the inner to midshelf is linear, and depth-averaged acce
leration is governed to lowest order by the difference between surface
and bottom stress alone. In this region, along-shelf geostrophic buoy
ancy-driven currents at similar to 5 m (calculated from surface densit
y) and along-shelf geostrophic wind-driven currents (computed from a d
epth-averaged linear model) are comparable in magnitude (similar to 10
-25 cm s(-1)).