Distortion of Internal Wave Patterns by Background Shear: A Case Study.
Abstract
A preliminary comparative study was made of the structure of numerically simulated internal wave patterns with and without background shear. The analysis focuses on two distinct aspects of the wave pattern: the energy envelope (that region of space within which appreciable density perturbations occur); and the phase information (the structure of the density perturbations within the energy envelope). Using real background oceanographic data, we examine how the energy envelope and phase information observed in the absence of shear are distorted by the presence of background shear. The relevant parameter for determining the relative importance of background shear is shown to be the bulk, rather than local, Richardson number, defined in terms of characteristic density and velocity variations over the characteristic dimensions of the wave pattern, rather than in terms of local derivatives of the background density and velocity profiles. Because of the influence of the larger scale, averaged properties of the shear profile on the wave propagation process, the net drift velocity of the energy envelope at any depth level does not accurately reflect the background current speed at that level. Sheer induced restrictions of the vertical extent of the energy envelope are shown to be consistent with elementary wave propagation arguments relating to the so-called critical layer phenomenon. Insofar as the phase information is concerned, we find significant coherence losses (relative to unsheared patterns) over several Brunt-Vaisala periods.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 26, 1979
- Accession Number
- ADA093813
Entities
People
- Thomas H. Bell Jr.
Organizations
- United States Naval Research Laboratory