Deep Cycle Turbulence in Atlantic and Pacific Cold Tongues

Multiyear turbulence measurements from oceanographic moorings in equatorial Atlantic and Pacific cold tongues reveal similarities in deep cycle turbulence (DCT) beneath the mixed layer (ML) and above the Equatorial Undercurrent (EUC) core. Diurnal composites of turbulence kinetic energy dissipation rate, epsilon, clearly show the diurnal cycles of turbulence beneath the ML in both cold tongues. Despite differences in surface forcing, EUC strength and core depth DCT occurs, and is consistent in amplitude and timing, at all three sites. Time-mean values of epsilon at 30 m depth are nearly identical at all three sites. Variations of averaged values of epsilon in the deep cycle layer below 30 m range to a factor of 10 between sites. A proposed scaling in depth that isolates the deep cycle layers and of epsilon by the product of wind stress and current shear collapses vertical profiles at all sites to within a factor of 2.

Automated summary

Multiyear turbulence measurements from oceanographic moorings in equatorial Atlantic and Pacific cold tongues reveal similarities in deep cycle turbulence beneath the mixed layer and above the Equatorial Undercurrent core. Despite differences in surface forcing, EUC strength and core depth DCT occurs, and is consistent in amplitude and timing, at all three sites. A proposed scaling in depth that isolates the deep cycle layers and of epsilon by the product of wind stress and current shear collapses vertical profiles at all sites to within a factor of 2.