Vorticity Dynamics near a Rocky Headland on the Inner-Shelf

Vorticity generation and evolution around headlands in the coastal ocean is a complicated process. Shallow water results in increased bottom drag, leading to significantly stronger forcing and damping than that found in the open ocean. Length- and time-scales are also short, leading to rapidly evolving processes that can be difficult to capture. An array of moored thermistors and co-located bottom-mounted ADCPs were deployed on the inner-shelf in 10- to 30-meter water depth in the vicinity of Point Sal, a 7.5 km-wide headland on California’s central coast near San Luis Obispo. The region is made up of complex, rocky bathymetry and characterized by strong tidal flows, sharp horizontal gradients, and a steady arrival of nonlinear internal waves. Vorticity is estimated at multiple locations using two methods. Groups of bottom-mounted ADCPs provide a localized time series of vorticity. Coordinated vessel surveys provide sparser time resolution but allow a transect of vorticity to be estimated. The different estimates are compared to identify the physical mechanism behind vorticity evolution. In a barotropic sense, vorticity is governed by a balance of advection, stretching, torques, and frictional dissipation. We show that the generation and evolution of vorticity is primarily governed by vortex stretching and advection. This is in contrast with previous studies in other regions, some of which neglected vortex stretching entirely. Impacts of vortex stretching on temperature variability are also investigated.