The ocean circulation over the Oregon shelf during spring and summer is dominated by the effects of coastal upwelling. Equatorward winds drive an offshore Ekman transport in the surface layer, which produces divergent flow at the coast and the upwelling of deeper, colder, nutrient-enhanced waters (Huyer, 1990). At the surface, the boundary between the upwelled and oceanic waters is often a front, and the upwelling-induced horizontal density gradients support an equatorward coastal jet (Mooers et al., 1976). The annual onset of persistent upwelling conditions often occurs abruptly in an event called the spring transition (Huyer, et al., 1979; Strub, et al., 1987), which is characterized by a persistent drop in coastal sea level and a tendency to persistence of equatorward wind forcing (punctuated by occasional wind reversals). Although fluctuations in the alongshore current have been shown to be coherent over large alongshore scales (Huyer et al., 1975), the local spatial variations in the currents are not well known, mainly due to our past inability to map the current field at high resolution in both space and time.

Kosro, P.M., J.A. Barth, and P.T. Strub. 1997. The coastal jet: Observations of surface currents over the Oregon continental shelf from HF radar. Oceanography 10(2):53–56, https://doi.org/10.5670/oceanog.1997.22.

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