Finescale parameterizations of turbulent dissipation

Abstract

Fine- and microstructure data from a free fall profiler are analyzed to test models that relate the turbulent dissipation rate (ε) to characteristics of the internal wave field. The data exhibited a factor of 140 range in squared buoyancy frequency (N2) with depth and uniform internal wave characteristics, consistent with the Garrett-Munk spectrum. The magnitude of ε and its variation with N(ε~N2) was best described by the dynamical model of Henyey et al. Data from wave fields that depart from the canonical GM description are also examined and interpreted with reference to the dynamical models. Of the dissipation predictions examined, those of the Henyey et al. model in which εN-2 scales as E2, where E is the nondimensional spectral shear level, were most consistent with observations. These results indicate that the kinetic energy dissipation rate (and attendant turbulent mixing) is small for the background Garrett and Munk internal wave conditions. Dissipation and mixing become large when wave shear spectral levels are elevated, particularly by high-frequency waves. -from Authors