Experimental Estimation of the Turbulent Energy Dissipation Rate in the Sea Subsurface Layer at Storm Conditions

Abstract

Rate of the turbulent energy dissipation arising due to the breaking surface waves is estimated based on the experimental data on near-surface turbulence. The studies were carried out on the oceanographic platform in the Black Sea coastal zone by the specialized measuring complex "Sigma-1". To analyze the data, specific hydrometeorological conditions including high wind speed and significant number of breaking waves were chosen from the total data array. The turbulent energy dissipation rate per unit of volume ε is calculated using the spectra of velocity fluctuations based on the Kolmogorov hypotheses on the inertial-range spectrum of turbulence. The dissipation rate per unit of area of the sea surface is calculated by the over depth integrating the values of ε defined on all the measurement horizons with their extrapolation up to the surface and bottom. The results provided by the experimental data are compared to the wave energy losses due to breaking calculated by the Phillips model (1985). The values of the breaking parameter b calculated under the assumption on its model dependence upon the wave number are smaller than the estimates obtained by the other authors. The second method of calculation implies an assumption that the breaking parameter is constant in every single experiment and does not depend on the wave number. The obtained values of b are of moderate spread and also smaller (within one order of magnitude) than the estimates obtained by the other authors. In this case the values of b are satisfactorily approximated by the constant bc ≈ 1.31·10 -4 . Discrepancy between the obtained results and those in the other sources can be conditioned by the differing waves' characteristics and methods for estimating the dissipation rate.

Model and Experimental Estimates of Vertical Mixing Intensity in the Sea Upper Homogeneous Layer

“…where b is the dimensionless parameter characterizing the intensity of breaking ; g is the free fall acceleration. Apparently, this approach is very promising, although the form of the dependence Λ(c) and the parameter b remain insufficiently studied [24][25][26][27].…”