FY 1980

Circulation in the Strait of Juan de Fuca: Recent oceanographic observations in the eastern basin

Holbrook, J.R., R.D. Muench, D.G. Kachel, and C. Wright

NOAA Tech. Report ERL 412-PMEL 33, NTIS: PB81-135352, 42 pp (1980)

In two field experiments conducted in the eastern Strait of Juan de Fuca during winter 1977–78 and summer 1978, 3-mo time series measurements of currents, over-the-water winds, shore winds, and water properties were obtained. From these data sets, the principal water motions are identified and described. Over time scales of 4 to 25 h, tidal currents dominate the current fluctuations and account for 58% to 99% of the current variance. Mean flow is characterized by an estuarine circulation that consists of a vigorous two-layer pattern with near-surface velocities directed seaward at 20 to 40 cm/s and deep layer velocities directed landward at 10 cm/s. Although local winds play a minor role in modifying near-surface circulation, coastal storms dramatically affect circulation in the eastern basin. During the winter experiment seven current reversals (up-strait subtidal flow) were observed for periods of 2 to 6 days and had eastward maximum velocities of 20 cm/s. The extent to which coastal winds affect flow in the eastern basin depends on their strength, duration, and direction. The reversals that propagated up-strait at speeds of 20 to 30 cm/s were observed as far as New Dungeness Spit, 135 km east of Cape Flattery. Coastal Ocean Dynamics Applications Radar (CODAR) surface drifter and current measurements during an intensive 4-day study period further delineate the spatial characteristics of a single coastally generated reversal. Although the long-term average near-surface flow is seaward, the effects of tidal currents and coastal storms and the resultant complex pattern of eddies, fronts, and shore-directed currents lead to a regime in which surface pollutants could impact the shore as far east as Whidbey Island.