A mesoscale eddy dipole in the offshore California Current

Abstract

There is a transition zone in the California Current system between inshore coastal and offshore oceanic flow. This transition zone is associated with the main core of the California Current and is populated with offshore mesoscale eddies. The structure of isolated eddies and dipole eddy pairs found within the transition zone is examined using water mass analysis (spiciness and dissolved oxygen). The analyses show that these offshore mesoscale eddies have cores which contain California Undercurrent water. These observations and independent observations of the Sitka eddy near Sitka, Alaska, support the conclusion that a bathymetrically induced instability of the California Undercurrent is a likely generation mechanism for the offshore eddies. This conclusion also is consistent with mathematical models of eddy generation in a subsurface, poleward baroclinic current. The similarity between long‐term mean conditions (CaICOFI), conditions observed during January 1981 and July 1985, and those of the Sitka eddy, coupled with the bathymetric effects, provides a plausible explanation for the recurrence of offshore mesoscale eddies at preferred locations within the transition zone.