Measurements and Models of Fine-Structure,Internal Gravity Waves and Wave Breaking in the Deep Ocean.

摘要

Measurements of horizontal and vertical current by propeller cluster current meters and temperature by thermistors mounted on a rigid array 8 m high and 20 m long moored in the oceanic main thermocline near Bermuda are interpreted in terms of thermocline-trapped internal wave modes in the presence of temperature and density fine-structure. Two turning-point uniformly valid asymptotic solutions to the internal wave equation are developed to describe the wave functions. Mode decay beyond the turning point in depth or frequency produces a sharp cutoff in vertical current spectra above the local buoyancy frequency N(z). An internal wave wavenumber-frequency spectral model describes the vertical current spectra and potential energy to horizontal kinetic energy ratios. The red wavenumber shape suppresses peaks in both these quantities at frequencies near N(z). The data are consistent with time-averaged horizontal isotropy of the wave field. A dip in the vertical current spectral at 0.5 cph not predicted by the model appears related to the bottom slope. Temperature fine-structure is modeled as a passive vertical field advected by internal waves. Quasi-permanent fine scale features of the stratification and vertically small-scale internal waves are indistinguishable in this study. Horizontal current fine-structure is also modeled as a passive field advected vertically by long internal waves. The model describes moored horizontal current spectra (least successfully at frequencies near N(z)) and finite-difference vertical shear spectra. Contours of temperature in depth versus time indicate possible mixing events.