Observations of Turbulence, Internal Waves and Background Flows: An Inquiry intothe Relationships between Scales of Motion

摘要

Oceanic profile data are used to examine the parameterization of turbulentdissipation due to internal waves. For observations exhibiting GM (MunK 1981) internal wave characteristics, the dissipation magnitude and its functional dependence upon wave energy level and buoyancy frequency was best described by the dynamical model of Henyey et al. (1986). For non-GM wave fields, dissipations were modeled most effectively by a frequency based correction to this model. ne Richardson number scaling model of Kunze et al. (1990) produced consistent dissipation estimates. Model agreement here appears a consequence of statistical dependence between velocity shear and strain, hypothesized to be an effect of turbulent fluxes. These fluxes can effect low wavenumber spectral amplitudes only in the limit of strong stratification, low average wave-frequency and Coriolis frequency. An internally consistent picture of mixing in the ocean results: Energy is transported through the internal wave spectrum to small vertical scales where it is dissipated via shear instability processes. We find background diffusivities small and independent of depth (<10 to the -5 sq m/s); heightened wave energy in the abyss associated with topographic features or larger scale flows appears needed for internal waves to cause the 1-10 x 10 to the -4 sq m/s diffusivities generally inferred from deep ocean hydrographic data.