Collaborative Research: The Heated Wind- and Wave-Driven Ocean Surface Boundary Layer: Synergistic Analyses of Observations and Simulations

University Of Delaware, Newark DE

Investigators

Abstract

The ocean's surface layer in contact with the atmosphere (or surface boundary layer -- OSBL) controls climate, weather, and Earth system dynamics by coupling the ocean and atmosphere through air-sea fluxes. Turbulence in the OSBL distributes biogeochemical and ecologically relevant tracers that are floatable (buoyant), such as plankton, bubbles, nutrients, oil, and microplastics. Wind and waves drive OSBL turbulence in several critical ways: Wind-generated ocean currents; wave-current interactions result in wind-aligned vortices, called Langmuir turbulence (LT); and breaking waves inject turbulent kinetic energy to the subsurface . The present conceptual and theoretical framework of wave-driven OSBL dynamics is largely based on conditions for which surface heat fluxes are assumed to be either neutral or conducive to overturn the surface water column. However, diurnal heating or rain events prevent overturning and are omnipresent over the world oceans. This project would use numerical simulations and analysis of existing data sets to explore the effects of surface waves on the stratified OSBL in surface heating conditions. The objectives of this study are to: (1) identify limitations of traditional surface boundary assumptions due to wave effects; (2) reveal the dynamics of wave effects on the heated OSBL, based on a systematic analysis of momentum, buoyancy, and turbulent kinetic energy; (3) integrate data and simulations to establish a turbulence regime diagram that reveals the conditions in which Langmuir turbulence (LT) and breaking wave effects affect OSBL dynamics; (4) perform an analysis of turbulence statistics to assess and proposes improved ocean mixing parameterizations. These new parameterizations will be applied to demonstrate the importance of wave effects on the transport of buoyant tracers during diurnal OSBL heating. The work will be relevant across many oceanographic and atmospheric sub-disciplines; support an early career researcher; train graduate students; and engage in outreach. The proposed research will test specific hypotheses: (1) wave effects on heated OSBL dynamics are significant and quantifiable through observations and simulations; (2) LT is essential for OSBL mixing but sufficiently strong heating generates favorable conditions for shear-driven turbulence due to jets; (3) breaking waves prevent flow laminarization in strong heating conditions; and (4) wave-driven mixing in heated OSBLs can be accurately represented in improved turbulent mixing parameterizations to capture accelerated jet transport and the deep submergence of buoyant tracers. The team has access to several extensive observational data-sets, from which they will be able to determine the presence of LT during surface heating and assess the impact of LT on OSBL dynamics. Numerical experiments will be conducted using Large Eddy Simulations (LES) which produce LT through vortex forcing and include effects from breaking waves. Based on results from a combined data, LES modeling analysis, physics-motivated and practical mixing parameterizations for the heated OSBL will be developed, assessed, and applied to transport of buoyant tracers, such as microplastics, plankton or oil. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.