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A new theory for Langmuir transport in the ocean mixed layer

Oct 22, 2025, 1:30 - 2:30 PM


Speaker: Eojin Kim, Harvard University

CLIM seminar_10222025_Kim

Title: A new theory for Langmuir transport in the ocean mixed layer 

Host: Timothy Delsole

Time: Wednesday, Oct 22, 1:30-2:30 PM

Location: Horizon Hall, Room 4014 (Email xdu5@gmu.edu for Zoom link)

 

Abstract: The ocean’s mixed layer plays a central role in controlling the exchange of momentum, heat, gases, and particulates between the ocean and the atmosphere. A striking feature of mixed-layer dynamics is the formation of spanwise-ordered, streamwise-aligned roll–streak structures (RSS), commonly known as Langmuir circulations, which develop under surface wind stress.  The coherence and long-range organization of Langmuir circulations suggest a modal instability, yet Eulerian shear from wind stress alone does not support an instability with RSS form.  However, in the presence of velocity fluctuations superposed on the Eulerian shear two instabilities are supported.  The first of these is the familiar Craik–Leibovich type 2 (CL2) instability, arising from interaction between the Eulerian shear forced by the surface wind stress and the irrotational Stokes drift arising from surface waves.  The second is the Reynolds stress (RS) torque instability arising from systematic organization of turbulent Reynolds stresses by the RSS..  While the CL2 instability is widely regarded as the mechanism underlying the formation of Langmuir circulations,  the RS torque instability is familiar in the context of wall-bounded shear flows, where there is no Stokes drift.  Here, we show that in the ocean mixed layer these two instability mechanisms operate synergistically, and we assess their relative contributions to RSS formation and the transport of momentum and tracers.

 

Bio: Eojin Kim is a PhD candidate in Department of Earth and Planetary Sciences at Harvard University. He received his B.S. in Engineering Science at UC Berkeley in 2019. His major research interests include understanding dynamics of coherent structures in turbulence. In geophysical contexts, those include understanding roll streak structures (RSS) in planetary boundary layers.

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