High vertical resolution measurements of the flow in the western equatorial Pacific reveal the vertical shear to be dominated by flow features that have a small vertical scale (O(10 m)). This is true for all the measurements we have taken over a 3 year period and differing ENSO states. Much of the measured turbulent activity is found to be associated with these small scale features, with the suggestion that mixing in the region is heavily influenced by the presence of this small scale activity. The level of mixing within and above the thermocline is strongly modulated by ENSO events, with the level of mixing being significantly greater during the observed La Niña event. Changes to the stratification above the thermocline during ENSO events play a major role in both changes to the level of turbulent activity and the effective vertical diffusion coefficient.

We investigate the characteristics of shear-generated turbulence in the natural environment by considering data from a number of cruises in the western equatorial Pacific. In this region, the vertical shear of the flow is dominated by flow structures that have a relatively small vertical scale of O(10 m). Combining data from all cruises, we find a strong relationship between the turbulent dissipation rate, , vertical shear, S, and buoyancy frequency, N. Examination of at a fixed value of Richardson number, Ri 5 N 2 =S 2 , shows that / u 2 t N for a wide range of values of N, where u t is an appropriate velocity scale which we assume to be the horizontal velocity scale of the turbulence. The implied vertical length scale, ' v 5 u t =N, is consistent with theoretical and numerical studies of stratified turbulence. Such behavior is found for Ri < 0.4. The vertical diffusion coefficient then scales as j v / u 2 t =N at a fixed value of Richardson number. The amplitude of is found to increase with decreasing Ri, but only modestly, and certainly less dramatically than suggested by some parameterization schemes. Provided the shear generating the turbulence is resolved, our results point to a way to parameterize the unresolved turbulence.

A developing MJO event in the tropical Indian Ocean triggered wind disturbances that generated inertial oscillations in the surface mixed layer. Subsequent radiation of near‐inertial waves below the mixed layer produced strong turbulence in the pycnocline. Linear plane wave dynamics and spectral analysis are used to explain these observations, with the ultimate goal of estimating the wave energy flux in relation to both the energy input by the wind and the dissipation by turbulence. The results indicate that the wave packets carry approximately 30–40% of the wind input of inertial kinetic energy, and propagate in an environment conducive to the occurrence of a critical level set up by a combination of vertical gradients in background relative vorticity and Doppler shifting of wave frequency. Turbulent kinetic energy dissipation measurements demonstrate that the waves lose energy as they propagate in the transition layer as well as in the pycnocline, where approaching this critical level may have dissipated approximately 20% of the wave packet energy in a single event. Our analysis, therefore, supports the notion that appreciable amounts of wind‐induced inertial kinetic energy escape the surface boundary layer into the interior. However, a large fraction of wave energy is dissipated within the pycnocline, limiting its penetration into the abyssal ocean.