Graduation date: 2006
The effects of alongshore variability in topography (banks and capes) and spatial variability in the wind forcing, including the wind-stress curl, on coastal ocean circulation are studied using a combination of observations and model simulations. Satellite sea surface temperature observations are used to describe the seasonal evolution of temperature fronts in the California Current System. The evolution is consistent with the seasonal cycle of wind forcing, but also reveals the profound influence of major capes in creating convoluted and offshore-diverted fronts. Although the greatest offshore excursion of fronts is found south of Cape Blanco, observations suggest that late in the upwelling season, the upwelling front (and jet) leaves the shelf to the north of the Cape, around Heceta Bank. This is supported by in situ observations obtained during the Coastal Ocean Advances in Shelf Transport (COAST) project, which depicted jet separation at Heceta Bank's downstream asymmetry with an average off-shelf transport around 0.7 Sv. Simulations exploring a large range in parameter space show that jet separation is expected to occur when the flow is strong (high Rossby number) and when the Burger number (the ratio of the squares of the internal Rossby radius of deformation and curvature of the topography) is close to one. Observations reveal that conditions at Heceta Bank during spring and summer are often nearly ideal for separation. The importance of the wind-stress curl to coastal circulation is also investigated. A region of upwelling-favorable wind-stress curl close to the coast downstream of a cape is shown to create a strong offshore intensification of the alongshore velocities, which helps jet separation via continuity and by creating potential vorticity contours that track far offshore of the cape. Stronger upwelling-favorable curl leads to earlier separation, while increasing the offshore extend of the region of strong curl leads to more separation. Finally, satellite scatterometer observations are used to show that the wind-stress curl is strongly enhanced around Cabo Frio, Brazil, during summer. At that time, curl-driven upwelling is as strong as coastal upwelling, which helps explain the observation that the coldest water along the coast is found near Cabo Frio.