Determination of the Rate of Dissipation of Turbulent Energy from Simultaneous Temperature and Velocity Shear Microstructure Measurements

Abstract

Spectra of turbulence have been examined for both temperature gradient and velocity shear. The data for this comparison are 10–15 m segments of vertical microstructure profiles (at depths of 5–100 m) obtained during the 1978 Joint Air Sea Interaction experiment (JASIN). From the simultaneous measurement of them two microstructure quantities, the universal spectral constant q (the least principal rate of strain of the velocity spectrum) has been determined to be 3.7 ± 1.5. As well, the dissipation rate has been calculated from the high-wavenumber cut-off of the temperature microstructure spectra (εB) and from velocity shear (εSH). For a range of values from 8 × 10−9 to 5 × 10−7 m2 s−3 these two measures, εB and εSH, agree to within a factor of 2 on average. And finally, estimates of ξθ (temperature dissipation rate), ε and mean temperature gradient have been used to estimate a mixing efficiency, Γ = 0.24.