Poleward flow off central California during the spring and summer of 1981 and 1984

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Abstract
Currents and winds measured over the continental shelf and upper continental slope during the first half of 1984 are analyzed to determine the character of the flow off central California (Point Conception to San Francisco). The mean flow was poleward from Point Conception to Point Sur, in opposition to the equatorward wind stress. The mean flow was equatorward north of Point Sur. Fluctuations in alongshore currents over the shelf were highly correlated with local winds everywhere except off Point Conception, where currents were not only uncorrelated with wind but also poorly correlated with currents farther north. North of Point Buchon there is evidence for poleward propagation of shelf current variability at 175–200 cm/s. The correlation between currents and local wind forcing dropped considerably beyond the shelf break, only 10–15 km offshore from the shelf moorings. During extended periods of weak equatorward winds, the poleward shelf flow south of Point Sur spreads farther offshore over the continental slope. A three week period of calm winds in July 1984 resulted in a 100‐km‐wide tongue of poleward flow extending 300 km along the California coast. Similar, but somewhat weaker, poleward surface flow occurred during the same period in 1981; a 2‐ to 3‐week period of calm winds in late June and early July 1981 resulted in a 100‐km‐wide tongue of poleward flow extending at least 150 km along the California coast. In contrast to the poleward flow on the shelf, which appears to be normal during spring and summer, the poleward surface flow observed over the slope in July 1981 and 1984 is unusual, based on historical hydrographic surveys off the central California coast. Poleward surface flow over the continental slope occurs seasonally in the winter but is not generally observed after February.