The physical structure of cold filaments near Point Arena, California, during June 1987
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Shipboard conductivity-temperature-depth, acoustic Doppler current profiler, and continuous temperature and salinity observations were made in the coastal transition zone off Point Arena, California (39-degrees-N, 124-degrees-W), during June 15-28, 1987, to describe the hydrographic structure and velocity fields associated with the cold filaments found there. An adaptive sampling plan was used to measure the properties of these filaments, guided in real time by satellite Advanced Very High Resolution Radiometer sea surface temperature imagery and feedback from the situ sensors. The primary feature observed was a large, cool (12.0-degrees-13.5-degrees-C), salty (32.7-33.0 psu) filament which extended over 200 km offshore from Point Arena and exceeded 500 m depth. This feature was bounded in the offshore direction by a continuous equatorward meander, with offshore velocities (60-87 cm s-1) on the northern edge of the cool filament and onshore velocities (69-92 cm s-1) along the southern edge, and persisted for at least 3 weeks. A second feature was advected into the study area from the north by an anticyclonic eddy offshore and later merged with the Point Arena filament. Smaller (30 km wide by 50-100 km long by 50-100 m deep) very cold (10.0-degrees-12.0-degrees-C) high salinity (> 33.0 practical salinity units (psu)) features were observed within the Point Arena filament, but persisted for only 6-10 days. The net volume transport of the larger feature was offshore at approximately 3 x 10(6) m3 s-1 and suggests it was fed by an inflow to the region from the north. The smaller features were correlated with burst of equatorward wind stress on an event by event basis but not with times of large-scale wind stress convergence. Surface drifters deployed during the experiment closely followed the surface dynamic topography. Some of the drifters followed the path of the offshore meander, while others moved south inshore.