Stalling and Dissipation of a Near-Inertial Wave (NIW) in an Anticyclonic Ocean Eddy: Direct Determination of Group Velocity and Comparison With Theory

Abstract

A near-inertial wave stalling and breaking in a critical layer was observed for a week by a pair of autonomous velocity and density profilers on concentric paths in an ocean mesoscale eddy. Profiler observations provide estimates of the eddy's vertical vorticity and shear, quantities needed to test theories of downward near-inertial wave (NIW) energy flux and loss from inertial wave–eddy interactions. The unique observations of the wave's intrinsic frequency (Formula presented.) and vertical wavenumber m provide a novel estimate of the vertical group velocity Cgz from changes in (Formula presented.) with respect to m. Shear, strain, energy flux convergence, and parameterized turbulence are all elevated near 140 m depth, near the bottom of the strongest eddy velocities. Our observations are consistent with a downgoing NIW's group velocity decreasing owing to wave–eddy interactions, providing important clues on global energetics of NIW mixing.