Atmosphere Ocean Science Colloquium

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Overturning and scouring in the upper ocean transition layer

Speaker: Alexis Kaminski, University of California, Berkeley

Location: Online

Date: Wednesday, December 1, 2021, 3:30 p.m.

Synopsis:

A crucial region of the ocean surface boundary layer (OSBL) is the strongly-sheared and -stratified transition layer (TL), where a diverse range of waves and instabilities are possible. Previous work suggests that these different waves and instabilities will lead to different OSBL behaviours, and so understanding which physical processes occur is key for modelling the TL. In this talk, I will present simulations of symmetric and asymmetric shear instabilities, and describe their dynamics in terms of two limiting stratified turbulence regimes: scouring, in which an initial interface remains intact, and overturning, which smears out initial density gradients. These simulations will then be compared with recent high-resolution observations of the North Pacific transition layer from a Lagrangian float deployed in Fall 2018, demonstrating the presence of both overturning and scouring dynamics driving OSBL evolution. Combined, the simulations and observations demonstrate the need to understand the mechanisms underlying ocean mixing.