California Sea Grant College Program

A shipboard current profiler, the Doppler Acoustic Log (DAL), is used to study the coastal and offshore circulation in a region of strong, upwelling favorable wind forc­ing off Northern California. Errors in the technique are discussed in some detail, and methods for extracting the signal are derived. Comparison is made between shipboard and moored current measurements.

The results from some 74 days of shipboard measurements are then discussed. Averaged measurements show a divergent mean cross-shore circulation with offshore flow near the surface and weak onshore flow below, a mean equatorward coastal jet whose position and intensity varies alongshore, and a poleward undercurrent flowing opposite to the mean wind forcing which has a maximum near the shelf break and surfaces close to the coast. The synoptic surveys reveal a complex current field which enhances the wind driven Ekman Exchange of coastal and offshore water properties in narrow regions of strong offshore flow. Two detailed surveys of tongues of cold, coastally upwelled water extending 250 km out to sea in July of 1981 and 1982 show they are being advected by offshore current jets up to 75 cm/sec in strength and over 100 m in depth. These jets transport in excess of 1.5 Sv. Closer to shore, the structure of the flow during a wind relaxation is also examined.