FY 1981

Circulation in the lower Cook Inlet, Alaska

Muench, R.D., J.D. Schumacher, and C.A. Pearson

NOAA Tech. Memo. ERL PMEL-28, NTIS: PB82-126418, 26 pp (1981)

Circulation in the lower Cook Inlet region has been described and discussed utilizing current observations obtained during October 1977–October 1978. The major circulation feature was a mean westerly flow which entered the region via Kennedy and Stevenson entrances, paralleled the 100-m isobath through the lower Inlet then exited the system via Shelikof Strait. Summer mean current speeds in this flow were 10–15 cm/s; winter speeds were 25–30 cm/s. A secondary circulation feature was present as southward flow which occupied the western portion of the lower Inlet. Summer current speeds here were 15–20 cm/s, while winter speeds were of order 10 cm/s. The westerly flow is driven in summer primarily by a baroclinic field consequent to coastal freshwater input (the Kenai Current), while in winter this flow is driven to a greater extent by wind-driven coastal convergence and possibly by an alongshore pressure gradient set up by the Alaskan Stream. The southward flow, driven by freshwater input into upper Cook Inlet, therefore is larger in summer when this input is greater. Mean flow in the eastern lower Inlet was weak and variable in all seasons. Low-frequency and tidal flow fluctuations were superposed upon the mean flow and in regions of low mean speeds controlled the instantaneous flow. The low-frequency fluctuations were associated with westerly flow through the system, and probably originated through meteorological disturbances on the continental shelf outside the Inlet. Tidal currents were large (70–100 cm/s) and primarily semidiurnal in the eastern portion of the lower Inlet and in Kennedy and Stevenson entrances. In the western Inlet, tidal currents were only half this magnitude, and in Shelikof Strait they were very small due to presence of an antinode near the mooring in northern Shelikof Strait. Tidal currents were aligned with the local channel bathymetry.