Intermittency of internal wave shear and turbulence dissipation

It is crucial to understand the extreme intermittency of ocean and lake turbulence and turbulent mixing in order to estimate vertical fluxes of momentum, heat and mass by Osborn-Cox flux-dissipation methods. Vast undersampling errors occur by this method when intermittency is not taken into account, Gibson (1990a, 1991ab). Turbulence dissipation and internal wave shear in the ocean are closely coupled. Often, oceanic turbulence is assumed to be caused by breaking internal waves. However, the extreme intermittency observed by Gregg et al. (1993), with intermittency factor I-S(4) approximate to 6 for 10 m internal wave shears S, strongly suggests that wave breaking is not the cause of turbulence but an effect. The usual assumption about the wave-turbulence cause-effect relationship should be reversed. Wave motions alone reduce intermittency. Oceanic turbulence increases intermittency as the result of it self-similar nonlinear cascade covering a wide range of scales, mostly horizontal, but no such nonlinear cascade exists for internal waves. Extremely large I epsilon and I chi measured for oceanic turbulence are in the range 3-7, Baker and Gibson (1987). These values are consistent with the third universal similarity hypothesis for turbulence of Kolmogorov (1962) and a length scale range over 3-7 decades from viscous or diffusive to buoyancy or Coriolis force domination, where the measured universal intermittency constant mu = 0.44; Gibson (1991a), is a result of singularities in multifractal turbulence dissipation networks and their degeneration, Bershadskii and Gibson (1994). The extreme intermittency of small scale internal wave shears in the ocean is a fossil turbulence remnant of the extreme intermittency of ocean turbulence, and the waves themselves may be fossil turbulence. Evidence that composite shear spectra and schematic temperature gradient spectra in the ocean reflect fossil turbulence effects, Gibson (1986), is provided by the decaying tidal sill temperature spectra of Rodrigues-Sero and Hendershott (1997).