![]() If the underlying region is statically stable or neutral, the interface between turbulent and non-turbulent fluid is very sharp, and remains so as the turbulence erodes the lower fluid by entrainment. Below the surface, a turbulent mixed layer develops. When the wind blows across the surface of the water, a tangential surface stress is developed both directly from the interfacial stress, and indirectly by the rate of momentum loss from the surface waves by such processes as wave breaking. ![]() This differentiation is useful, not only conceptually but also observationally since the mechanisms of energy transfer (in both physical and Fourier space) are essentially different. A distinction is drawn between turbulence in a stably stratified fluid on the one hand and random field of internal gravity waves on the other. The characteristic properties of turbulent motions are that they possess a random distribution of vorticity in which there is no unique relation between the frequency and wave number of the Fourier modes that they are diffusive and dissipative. Not all of the random motions found in the ocean, however, can be described properly as turbulence. ![]() Again, the response of the ocean to large-scale wind and thermal disturbances and the development of ocean currents is dependent on the transfer of matter, momentum and energy by irregular smaller scale motions of one kind or another. For example, the interplay between the ocean stratification and the diffusive turbulent motions is often crucial in determining the structure of each. In the ocean, no less than in the atmosphere, is its influence widespread. Turbulence is one of the most ubiquitous phenomena in all of fluid mechanics. ![]()
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