Distinguishing Propagating Waves and Standing Modes: An Internal Wave Model

Abstract

Abstract This paper examines high-frequency (0.1-0.5 cph) internal waves, waves previously characterized by the Garrett and Munk spectral fits (GM72, GM75, GM79) as being vertically symmetric propagating waves (or equivalently “smeared” standing modes—GM72). Coherences at large vertical separations measured with deep sea moorings show significant differences from the GM79 predictions. The differences can be explained by modifying the purely propagating model to one that includes the spectral truncation and phase locking associated with a spectrum of standing modes. A model consisting of only standing modes, however, is also inadequate, whereas a more general spectral model, which effectively allows both propagating waves and standing modes, is not. These results show that much of the simplicity of the GM79 spectral fit can be attributed to lack of spectral resolution in the set of measurements to which the GM models were fit. The GM79 simplicity is not an intrinsic property of the internal wave field.