Observed interaction between oceanic internal waves and mesoscale eddies

Abstract

Measurements from arrays of moored current meters taken during the Mid-Ocean Dynamics Experiment (MODE) are analyzed, using short-term spectral analysis. A weak variability in space and time is detected in the internal wave continuum, as well as some horizontal anisotropy. It is suggested that the observed anisotropy is induced by the weak interaction between internal waves and mesoscale motions in a manner consistent with the weak interaction theory of $\text{>u}\text{̈}$ (Hamburger Geophysikalische Einzelschriften23, 1974). The interaction appears to be essentially local in space and time. It is shown that the internal wave continuum contributes positively to the horizontal diffusion of mean flow momentum, and is characterized by a relaxation time of the order of 1 to 4 days in the vicinity of the main thermocline. From observed correspondences between the fluctuations in total internal wave energy and square mean vertical shear, an estimate of the vertical eddy viscosity v_ν induced by internal waves is attempted, suggesting a large value for v_ν in the mid-ocean thermocline, maybe as high as 10³ cm² s⁻¹.