Near-Surface Turbulence and Thermal Structure in a Wind-Driven Sea

Abstract

Ocean surface turbulence at high sea states is evaluated using heat as a naturally occurring passive tracer. A freely drifting instrument with a mechanically driven temperature profiler, fixed depth thermistors, and conductivity cells was used to monitor breaking wave activity and fine-scale temperature structure within the upper 2 m of the water column. The combination of temperature profiles and independent heat flux measurements demonstrate the presence of wave-enhanced turbulence and the effects of subsurface advection due to Langmuir circulation. The turbulence length scale, extracted from the temperature profile fine structure, suggests a surface value significantly smaller than previously reported. A Prandtl-type mixing length model matched with a surface energy flux due to wave breaking and the observed turbulent length scale is consistent with the authors? observations. Both advection and enhanced diffusion are reconciled in a two-dimensional model of the upper-ocean boundary layer, providing a framework for studying Langmuir circulation and upper-ocean turbulence in terms of the measured temperature structure.