An Investigation Of The Statistical Characteristics Of Small-scale Turbulence In The Ocean

The turbulent kinetic energy(TKE)dissipation rate is the rate of the TKE conversion into the internal energy(heat)due to molecular viscosity.It is a useful measure of turbulence intensity and is central to ocean mixing studies.The microstructure profiler can be used to obtain estimates of the TKE dissipation rate by measuring microscale velocity shear.It is the state-of-the-art instrument for turbulence measurements in the ocean.Based on microstructure profiling measurements and results of the Direct Numerical Simulation(DNS)of quasi-isotropic turbulence,this thesis investigate the statistical characteristics of small-scale turbulence in the ocean.An integrated analysis of the profiling measurements at several locations in the world's oceans suggests that,the probability density function(PDF)of the estimated TKE dissipation rate deviates substantially from the classical Lognormal distribution,while the three-parameter Burr distribution(Burr ?)fits the data well.The latter can also give better estimates of the median value of the measured TKE dissipation rate.An analysis of the data processing procedures of microstructure profiling measurements suggests that,integration of shear spectrum in the estimation of TKE dissipation rate changes its statistical nature.In fact,the TKE dissipation rate does conform to the Lognormal distribution when the conditions of the Gurvich-Yaglom model are satisfied.Based on DNS data of quasi-isotropic turbulence,we further analyzed the rationality and conditions of the isotropic turbulence assumption,which is commonly used in the analysis of microstructure profiling data.The results suggest that it is valid only when a proper scale is chosen for spatial averaging.