Mixing Efficiencies in Turbulent Tidal Fronts: Results from Direct and Indirect Measurements of Density Flux

Abstract

The authors report direct measurements of density flux at a single depth in a turbulent tidal flow, made by towing a CTD beside the vertical beam of a modified acoustic Doppler current profiler. The direct flux estimates are compared with indirect estimates of density flux based on simultaneous microscale profiler measurements of ? and ?, dissipation rates of turbulent kinetic energy and of temperature variance, respectively. Two mixing efficiency estimates are made using Γd from the ratios of indirect flux estimates and Γo from the ratio of direct to ? flux estimates. The analysis indicates that ? Γd is no different from that determined in other open ocean experiments and is independent of the sign of the flux ? Γ d < |Γo|, regardless of the sign of the flux ? Γo (flux > 0) < |Γo| (flux < 0). The consequences for interpretation of ocean microstructure flux estimates are discussed.