April 18, 2019  

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Buijsman, International Research Group Examine Internal Ocean Waves

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In a study on the formation and fate of internal waves in the South China Sea, these images taken from the research project show, in the top panel, the east-west velocities at the ridge computed in a 2D model, with red to the right, and in the bottom panel, the turbulent dissipation in a 1,600 foot tall breaking wave trapped at the ridge. The horizontal lines mark the density interfaces, and the horizontal stick marks the velocity of the surface tide, which is to the right.

Dr. Maarten Buijsman, an assistant professor in The University of Southern Mississippi’s Department of Marine Science, was part of an international research team whose work was featured in the article “The formation and fate of  internal waves in the South China Sea” published in the May 7 issue of Nature. The project is the first of its kind to examine and present the life cycle of internal ocean waves reaching 1,600 feet in height.

Buijsman worked with researchers that included physical oceanographers at Scripps Institution of Oceanography at the University of California, San Diego on the study, conducted at the Luzon Strait between Taiwan and the Philippines. The sea’s internal waves are the largest of their kind in the world, and occur at the horizontal interfaces between warm and light and cold and heavy water layers. The waves are generated by the surface tide that propagates across the Luzon ridges.

“The overarching research question is ‘where do these internal waves dissipate?’ Do they dissipate close to the source, in the middle of the ocean, or do they propagate 1000s of km all the way across the ocean to dissipate at the continental shelves?,” Buijsman said. “The dissipation coincides with underwater turbulent wave breaking, like in the surf zone, and causes the vertical mixing of water masses.

“The location where they break is relevant for climate models. Climate models do not resolve the waves. Hence, the water mass mixing they cause needs to be parameterized. Where this parameterized mixing is applied in the model affects the global ocean circulation, and the future climate in climate sensitivity studies.”

Buijsman said the study shows at least 60 percent of the energy converted from the surface tide radiates away as internal waves from the steep ridges of Luzon Strait, providing information relevant for climate model studies.  

“My task in this work was the application of two-dimensional and three-dimensional hydrodynamic models to better understand the local dissipation (the 40%),” Buijsman said. “I also discovered interesting standing internal wave patterns between the ridges, which cause a clockwise energy flux spiral.”

Buijsman’s research interests include tidal internal wave generation and breaking at steep topography, propagation, and dissipation; wave drag parameterizations in global models; and estuarine physics and sediment transport. For more information about his research and publications, visit https://sites.google.com/site/maartenbuijsman/. For information about the Southern Miss Department of Marine Science, visit http://www.usm.edu/marine.