Synoptic three-dimensional circulation in an onshore-flowing filament of the California Current

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Abstract

Hydrographic (CTD and XBT casts) and Lagrangian particle drift (satellite-tracked mixed layer drifters) measurements taken off Southern California and northern Baja California in July 1985 are in the region where, historically, a stable, broad onshore flow is indicated in the 0/500 db relative dynamic topography. A 50 km wide onshore-flowing filament of cold and low-salinity water is resolved by the new measurements. Water mass properties (temperature, salinity and spiciness) are used to trace the different water masses and describe the circulation in the surveyed region. A comparison of the 15/300 db relative geostrophic currents to the drifter-inferred velocities shows a significant absolute geostrophic flow at the 300 db level, with coherent patterns similar to the surface mesoscale circulation. Estimates of vorticity calculated from the geostrophic and Lagrangian data are in qualitative agreement. Surface divergence and the implied vertical velocities of the order of 0.5 m day−1 are resolved at scales of 50–100 km. The spatial distribution of these estimates shows significant upwelling within the core of the filament.

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