Stochastically forced current fluctuations in vertical shear and over topography

Abstract

The effects of constant vertical shear of zonal velocity, uniform meridional bottom slope, and a deep meridional wall (representing the Mid‐Atlantic Ridge) on the response of a linear two‐layer quasi‐geostrophic ocean to stochastic wind stress curl forcing are investigated. The model is motivated by discrepancies in energy levels and distributions between recent observations and a similar model without shear or topography that predicted remote coherences relatively well. The results indicate that the presence of mean shear can significantly enhance the wind‐generation of surface‐intensified oceanic kinetic energy at frequencies above the zero‐shear cutoff for free baroclinic waves. The primary effect of the sloping topography is enhanced barotropic response near the barotropic topographic Sverdrup resonance, where topographic and planetary potential vorticity gradients cancel. The wall inhibits the barotropic response and increases coherences on the mooring side of the wall. Remote coherences for 49‐day period fluctuations are due to long barotropic waves as in the previous model, so the present model only partially reconciles the previous discrepancies.