The physical structure of cold filaments near Point Arena, California, during June 1987

Abstract

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°N, 124°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 in situ sensors. The primary feature observed was a large, cool (12.0°–13.5°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°–12.0°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 ∼3 × 106 m3 s−1 and suggests it was fed by an inflow to the region from the north. The smaller features were correlated with bursts 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.

SST patterns and dynamics of the southern Senegal‐Gambia upwelling center

“…During the upwelling season, they exhibit numerous patterns and features that seem repetitive and/or very persistent in time. Filaments are often absent or broad with edges smoother than can be observed, e.g., in the California current system [Ramp et al, 1991]. An explanation valid for the entire Canary system attributes this weak mesoscale variability and frontality to the compensations effects between salinity and temperature [Marchesiello and Estrade, 2009], which is stronger than in other systems.…”

Annual cycle of clupeiform larvae around Gran Canaria Island, Canary Islands

“…However, upwelling filaments originating from the north‐western coastal area of the African continent are flows of cold, relatively fresh water rich in nutrients. Filaments are originated either (i) by the presence of mesoscale eddies which draw recently upwelled waters away from the coast or (ii) by the meandering of the upwelling front, which entrains upwelled waters nearshore and creates cold water filaments (Ramp et al. , 1991; Strub et al.…”

Satellite observation of sharp frontal shear instabilities and surface jets in the Mediterranean Sea

“…A particularly interesting case is that of transient cold filaments observed off coastal areas. For a detailed overview, see Washburn and Armi (1988), Rienecker and Mooers (1989) and, more recently, Ramp et al (1991), Kostyanoy (1991;1996), Kostyanoy and Boubnov (1995), Moore and Murdoch (1993), and Barton et al (1993). In all these studies, irrespective of the elementary physical mechanism originating the phenomenon, filament space scales are found to be 100-300 km in length, 10-20 km in width, and 50-100 m in thickness; the resulting time scales are of a few weeks, and typical velocities are 10-50 cm/s.…”