The formation and fate of internal waves in the South China Sea


Matthew H. Alford, Scripps Institution of Oceanography
Thomas Peacock, Massachusetts Institute of Technology
Jennifer A. Mackinnon, Scripps Institution of Oceanography
Jonathan D. Nash, Oregon State University
Maarten C. Buijsman, University of Southern Mississippi
Luca R. Centuroni, Scripps Institution of Oceanography
Shenn Yu Chao, University of Maryland, College Park
Ming Huei Chang, Institute of Oceanography, National Taiwan University
David M. Farmer, University of Rhode Island
Oliver B. Fringer, Stanford University
Ke Hsien Fu, National Sun Yat-Sen University
Patrick C. Gallacher, NASA Stennis Space Center
Hans C. Graber, University of Miami
Karl R. Helfrich, Woods Hole Oceanographic Institution
Steven M. Jachec, Florida Institute of Technology
Christopher R. Jackson, Global Ocean Assoc.
Jody M. Klymak, University of Victoria
Dong S. Ko, NASA Stennis Space Center
Sen Jan, Institute of Oceanography, National Taiwan University
T. M. Shaun Johnston, Scripps Institution of Oceanography
Sonya Legg, Princeton University
I. Huan Lee, National Sun Yat-Sen University
Ren Chieh Lien, University of Washington
Matthieu J. Mercier, Institut de Mécanique des Fluides de Toulouse
James N. Moum, Oregon State University
Ruth Musgrave, Scripps Institution of Oceanography
Jae Hun Park, Korea Institute Of Ocean Science & Technology
Andrew I. Pickering, University of Washington
Robert Pinkel, Scripps Institution of Oceanography
Luc Rainville, University of Washington
Steven R. Ramp, Soliton Ocean Services
Daniel L. Rudnick, Scripps Institution of Oceanography
Sutanu Sarkar, University of California, San Diego
Alberto Scotti, The University of North Carolina at Chapel Hill
Harper L. Simmons, University of Alaska Fairbanks
Louis C. St Laurent, Woods Hole Oceanographic Institution

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Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking, they affect a panoply of ocean processes, such as the supply of nutrients for photosynthesis1, sediment and pollutant transport2 and acoustic transmission3; they also pose hazards for man-made structures in the ocean4. Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their sources before breaking5, making it challenging to observe them and to include them in numerical climate models, which are sensitive to their effects6,7. For over a decade, studies8-11 have targeted the South China Sea, where the oceans' most powerful known internal waves are generated in the Luzon Strait and steepen dramatically as they propagate west. Confusion has persisted regarding their mechanism of generation, variability and energy budget, however, owing to the lack of in situ data from the Luzon Strait, where extreme flow conditions make measurements difficult. Here we use new observations and numerical models to (1) show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena, (2) reveal the existence of gt;200-metre-high breaking internal waves in the region of generation that give rise to turbulence levels >10,000 times that in the open ocean, (3) determine that the Kuroshio western boundary current noticeably refracts the internal wave field emanating from the Luzon Strait, and (4) demonstrate a factor-of-two agreement between modelled and observed energy fluxes, which allows us to produce an observationally supported energy budget of the region. Together, these findings give a cradle-to-grave picture of internal waves on a basin scale, which will support further improvements of their representation in numerical climate predictions.

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