Internal Wave Generation in the Equatorial Undercurrent

The generation of internal waves in the equatorial undercurrent is studied using a large-eddy simulation (LES) model. The model is forced with a constant easterly windstress and diurnal heating and cooling. Internal waves are generated with typical horizontal wavelengths of about 250 m, consistent with observations and comparable to the wavelengths of the most unstable modes from linear instability analysis. The internal waves exhibit a diurnal cycle below the boundary layer, or well below the mixed layer. The equatorial undercurrent (EUC) shear is crucial for the generation of these “long” internal waves. The range of diurnal variation of the wave energy (or equivalently, the isotherm displacement) is also consistent with observations. The wave energy is highly correlated with turbulence dissipation in the stratified regions of the boundary layer, in agreement with observations. The wave energy flux below the boundary layer has a maximum value of about 0.4 mW/m near the core of the EUC. The wave energy flux into the deep ocean is about one order of magnitude smaller. The interaction of nighttime convection with the EUC does not contribute significantly to the internal wave field in the deep ocean.