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We formulate an expression for the turbulent kinetic energy dissipation rate,ϵ, associated with shear‐generated turbulence in terms of quantities in the ocean or atmosphere that, depending on the situation, may be measurable or resolved in models. The expression depends on the turbulent vertical length scale,ℓ_v, the inverse time scaleN, and the Richardson numberRi = N²/S², whereSis the vertical shear, withℓ_vscaled in a way consistent with theories and observations of stratified turbulence. Unlike previous studies, the focus is not so much on the functional form ofRi, but the vertical variation of the length scaleℓ_v. Using data from two ∼7‐day time series in the western equatorial Pacific, the scaling is compared with the observedϵ. The scaling works well with the estimatedϵcapturing the differences in amplitude and vertical distribution of the observedϵbetween the two times series. Much of those differences are attributable to changes in the vertical distribution of the length scaleℓ_v, and in particular the associated turbulent velocity scale,u_t. We relateu_tto a measure of the fine‐scale variations in velocity,. Our study highlights the need to consider the length scale and its estimation in environmental flows. The implications for the vertical variation of the associated turbulent diffusivity are discussed.

Numerical experiments show that in a zonally symmetric model of a tropical ocean forced only by transient winds both inertia‐gravity wave activity and the energy dissipation rate have a pronounced maximum in the pycnocline close to the equator regardless of the latitudinal distribution of the energy input into the ocean's mixed layer. We consider a number of factors that determine the spatial distribution of mixing and find that equatorial enhancement is due to a combination of three factors: a stronger superinertial component of the wind forcing close to the equator, wave action convergence at turning latitudes for equatorially trapped waves, and nonlinear wave‐wave interactions between equatorially trapped waves. The most important factor is wave action convergence at turning latitudes.

Global warming may modify submesoscale activity in the ocean through changes in the mixed layer depth (MLD) and lateral buoyancy gradients. As a case study we consider a region in the NE Atlantic under present and future climate conditions, using a time‐slice method and global and nested regional ocean models. The high resolution regional model reproduces the strong seasonal cycle in submesoscale activity observed under present‐day conditions. Focusing on the well‐resolved winter months, in the future, with a reduction in the MLD, there is a substantial reduction in submesoscale activity, an associated decrease in kinetic energy (KE) at the mesoscale, and the vertical buoyancy flux induced by submesoscale activity is reduced by a factor of 2. When submesoscale activity is suppressed, by increasing the parameterized lateral mixing in the model, the climate change induces a larger reduction in winter MLDs while there is less of a change in KE at the mesoscale. A scaling for the vertical buoyancy flux proposed by (Fox‐Kemper et al., 2008; doi:10.1175/2007JPO3792.1) based on the properties of mixed layer instability (MLI), is found to capture much of the seasonal and future changes to the flux in terms of regional averages as well as the spatial structure, although it over predicts the reduction in the flux in the winter months. The vertical buoyancy flux when the mixed layer is relatively shallow is significantly greater than that given by the scaling based on MLI, suggesting during these times other processes (besides MLI) may dominate submesoscale buoyancy fluxes.