Subtidal to Infra-Gravity Variability of Turbulent Stresses in a Mid-Latitude Stratified Inner-Shelf

We describe the temporal variability and the vertical structure of turbulent stresses across a stratified, mid-latitude inner shelf off Central California, using moored data from the Inner Shelf Dynamics Departmental Research Initiative (ISDRI), funded by the Office of Naval Research (ONR). The dataset consists of five upward-looking, five-beam ADCPs recording data at 1 Hz or 8 Hz and encompasses an approximately 60-days period (09-10/2017). Direct measurements of the variance of the along-beam velocities are used to estimate the covariances between the cross-shelf, along-shelf and vertical velocity components, and hence the turbulent stresses (vertical momentum fluxes). The dominant signal associated with surface gravity waves is removed by exploiting the vertical coherence of the wave orbital velocity predicted by linear theory with the Adaptive Filtering Method. The tidal, supertidal and subtidal parts of the signal are filtered and the turbulent stresses of internal bores, solitary waves and wind-driven mesoscale currents are described, as well as the phase-averaged tidal currents and turbulent vertical viscosity coefficients. These results may inform better parameterizations for turbulent friction in coastal primitive-equation models and help advance our understanding of the cross-shelf structure of the depth-dependent momentum balance within the stratified coastal ocean, as well as its complex dependence on wind and tidal forcing.