A Dynamical Description of Fall and Winter Mean Current Profiles over the Northern California Shelf*

Abstract

Abstract Fall and winter mean current profiles from a midshelf (water depth ∼90 m) northern California site exhibit a similar vertical structure for several different years. The alongshelf flow is poleward with a maximum velocity of 5–10 cm s−1 in the middle or upper water column. There is an offshore flow of about 2 cm s−1 in the upper 20–30 m, an onshore flow of about 2 cm s−1 in the interior (depths 35–65 m), and an offshore flow of about 1 cm s−1 within 20 m of the bottom. Profiles are similar for averages over timescales from weeks to months. Mean current profiles at other midshelf sites along northern California and two sites off Peru also have a similar vertical structure. The vertical shear in the mean alongshelf flow is geostrophic throughout the water column, that is, in thermal wind balance with the cross-shelf density gradient. For timescales of a week or longer the thermal wind balance extends to within 1 m of the bottom and reduces the mean near-bottom alongshelf flow to 1 cm s−1 or less. Th...