Seasonal variability in meanders of the California Current System off Vancouver Island

Abstract

Satellite infrared images taken over the past few years reveal seasonal variations in the meanders of the California Current System (CCS) off Vancouver Island. The CCS exhibits meanders with wavelength between 120 and 150 km in both winter and spring, when the upper ocean current all flows northwestward or southeastward, respectively. In summer, the CCS includes the California Undercurrent, which flows northwestward beneath the southeastward surface current and has shorter wavelength (75–80 km) meanders. Around the end of August, these shorter scale meanders are engulfed by the longer 150 km meanders. Finally, in the fall, eddies are detached from the offshore extensions of the longer meanders. A linear stability theory using a four‐layer model of the CCS successfully predicts the wavelengths in the winter and spring, but not in the summer and fall. The meander evolution observed in summer and fall is instead simulated by using a nonlinear numerical model in a domain with topographic obstacles selected to match the alongshore variations in the continental slope. The topographic features with a spatial periodicity of 75 km act as a trigger to initiate the short wavelength (75 km) meanders; following this, these 75 km meanders grow because of baroclinic instability. The 75‐km meanders, which have grown to large amplitudes, are replaced by longer (150 km) meanders because of nonlinear interactions between these two scales of meanders. Cyclonic eddies are finally shed from the longer meanders.