Generation and propagation of nonlinear internal waves in sheared currents over the Washington Continental Shelf

TitleGeneration and propagation of nonlinear internal waves in sheared currents over the Washington Continental Shelf
Publication TypeJournal Article
Year of Publication2018
AuthorsHamann M.M, Alford MH, Mickett J.B
JournalJournal of Geophysical Research-Oceans
Volume123
Pagination2381-2400
Date Published2018/04
Type of ArticleArticle
ISBN Number2169-9275
Accession NumberWOS:000434131900005
Keywordsandaman sea; dissipation; energy; generation; monterey submarine-canyon; nonlinear internal wave; oceanography; propagation; Shear; solitary waves; solitons; south china sea; sulu sea; tidal; tides; transport; turbulence
Abstract

The generation, propagation, and dissipation of nonlinear internal waves (NLIW) in sheared background currents is examined using 7 days of shipboard microstructure surveys and two moorings on the continental shelf offshore of Washington state. Surveys near the hypothesized generation region show semi-diurnal (D2) energy flux is onshore and that the ratio of energy flux to group speed times energy (F/cgE) increases sharply at the shelf break, suggesting that the incident D2 internal tide is partially reflected and partially transmitted. NLIW appear at an inshore mooring at the leading edge of the onshore phase of the baroclinic tide, consistent with nonlinear transformation of the shoaling internal tide as their generation mechanism. Of the D2 energy flux observed at the eastern extent of the generation region (13318 Wm(-1)), approximately 30% goes into the NLIW observed inshore (3611 Wm(-1)). Inshore of the moorings, 7 waves are tracked into shallow (30-40 m) water, where a vertically sheared, southward current becomes strong. As train-like waves propagate onshore, wave amplitudes of 25-30 m and energies of 5 MJ decrease to 12 m and 10 kJ, respectively. The observed direction of propagation rotates from 30 degrees N of E to approximate to 30 degrees S of E in the strongly sheared region. Linear ray tracing using the Taylor-Goldstein equation to incorporate parallel shear effects accounts for only a small portion of the observed rotation, suggesting that three-dimensionality of the wave crests and the background currents is important here.

DOI10.1002/2017jc013388
Short TitleJ Geophys Res-Oceans
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