Effects of surface-gravity waves on inner-shelf circulation along the central Oregon coast during summer.

Shelf-wide circulation in the California current along the Pacific Northwest coast of North America is dominated by wind forcing during the summer upwelling season. However, large surface-gravity waves also exist in the region, normally propagating onshore from the northwest during summer, driving an energetic surf zone. The effects of surface-gravity waves on inner-shelf upwelling circulation are investigated using observations from a bottom-mounted acoustic wave and current profiler. The instrument, a NORTEK AWAC, was deployed on a bottom lander at two inner-shelf stations, in water-depths of 15 and 12 m respectively, along the central Oregon coast during the summer of 2005. Sub-tidal, cross-shore and along-shore currents during both deployments were generally consistent with upwelling circulation. Depth-averaged, along-shore velocities were positively correlated with the local wind stress, as was cross-shore surface transport at the 15 m site. However, cross-shore surface transport at the 12 m site was not correlated with the wind. Significant wave heights and wave periods during the summer averaged 1-2 m at 6-8 s with numerous peak events reaching 3-5 m at 10-13 s. Comparing the measured wave climate with offshore, open-ocean wave climates from NOAA NBDC wave buoys shows that similar conditions existed throughout the region. However, waves propagating from the buoy to the lander had consistently smaller waveheights at the lander, indicating that significant dissipation occurs as the waves shoal. The source of this energy loss, and it's effect on local circulation are investigated using simple wave-transformation models and circulation models which include wave-current interactions.