On the parameterization of equatorial turbulence

Abstract

Profiles of currents, density, and microstructure were obtained in the Pacific Ocean on and near the equator at 140°W in late 1984 as part of the Tropic Heat program. During a 4½‐day time series on the equator, the shear zone above the core of the undercurrent had very low mean Richardson numbers, Ri , between ¼ and ½. Average turbulent dissipation rates, ε, were high in this zone, ≈ 10 −7 W kg −1 , and varied by a factor of 100 between minima in the early afternoon and maxima at night. The signal reached to 90 m, well into the stratified zone. Eddy coefficients, K , were low at high Ri , and gradually increased as Ri decreased, until they rose dramatically near Ri = ½. The observed K ( Ri ) relations are specific to time, location, and temporal and spatial resolution of the data.