The Analysis Of Turbulent Characteristics In The Bottom Boundary Layer Of Monterey Canyon

There are various scales of motions in ocean, and energy usually propagates from large scales to small scales, finally dissipates as turbulence. Turbulence is a small-scale chaos motion which is different from the laminar flow, and it widely exists in atmosphere, ocean and engineering. Turbulence has complex and diverse structures with intermittency in time and space, randomness, high vorticity, high nonlinearity, strong mixing and diffusivity. Because of its complexity, turbulence is hard to measure directly, and the lack of wide-domain and long-time observation leads to unclear structure and mechanism. For the needs of long-time continuous measurements, this thesis is based on the ADV data from April24to October25in the Bottom Boundary Layer (BBL) of Monterey Canyon (MC) to analyze the tidal currents and turbulent characteristics.The results show that in BBL there is a strong contra-rotating tidal current up to0.398m/s with a dominant semidiurnal period, diurnal period and1/3diurnal period. The daily mean currents suggest the15-days and5-days period in May and August and about2to4-days period in June and October. The monthly mean data suggest during the observation, the bottom current is strongest in May and gets weaker in September and October; in the BBL, the horizontal flow is often westward and southward and upwelling always exists; from April to June, the westward flow is stronger than southward flow, and then contrary.In the BBL of MC, the first-order fluctuations reveal quasi-normal distribution, second-order variance is positively skewed with high kurtosis, and second-order covariance is negatively skewed with high kurtosis. At the moment of minimum velocity, the simulated independent timescales of w’and u’w’ are5.5s and3s, respectively; at the moment of maximum velocity, the timescales are2.5s and2s, respectively; between the two conditions, the autocorrelation shows no evident peak.Turbulence is highly anisotropic in the BBL of MC. The difference between horizontal components and vertical component of turbulent fluctuation intensity could be an order of magnitude; friction velocity and drag coefficient varies between6.50X10-3-2.32×10-2m/s and6.30×10-3-4.36×10-2, respectively, and the month-averaged minimum happens in July; the dissipation rate ranges between1.09×108-6.62×10-5W/kg. These turbulent characteristics show obvious cycle characteristics such as the prominent semidiurnal period. Besides, the fluctuation intensity and dissipation rate has diurnal and1/3diurnal period, and the dissipation rate also shows a quarter diurnal period; friction velocity and drag coefficient has diurnal and1/4diurnal period. Fluctuation intensity, friction velocity and drag coefficient all show8-days and4-days period. To validate the models ε-u and ε-et with elevated dissipation rate, friction velocity and turbulent kinetic energy, the results shows that the traditional values for model are as about10times as the calculated correction factor, implying that the theory models are not appropriate for the BBL of MC.