Near-inertial waves and turbulence driven by the growth of swell

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  • 1 Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
  • 2 Integrated Applied Mathematics and Mechanical Engineering, University of New Hampshire, Durham, NH, USA
  • 3 Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
  • 4 Service de Physique de l’Etat Condense, Commissariat á l’Energie Atomique Saclay, CNRS UMR 3680, Universit è Paris-Saclay, France
  • 5 Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
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Abstract

Between 5 and 25% of the total momentum transferred between the atmosphere and ocean is transmitted via the growth of long surface gravity waves called ‘swell’. In this paper, we use large eddy simulations to show that swell-transmitted momentum excites near-inertial waves and drives turbulent mixing that deepens a rotating, stratified, turbulent ocean surface boundary layer. We find that swell-transmitted currents are less effective at producing turbulence and mixing the boundary layer than currents driven by an effective surface stress. Overall, however, the differences between swell-driven and surface-stress-driven boundary layers are relatively minor. In consequence, our results corroborate assumptions made in Earth system models that neglect the vertical structure of swell-transmitted momentum fluxes and instead parameterize all air-sea momentum transfer processes with an effective surface stress.

Corresponding author: Gregory L. Wagner, wagner.greg@gmail.com

Abstract

Between 5 and 25% of the total momentum transferred between the atmosphere and ocean is transmitted via the growth of long surface gravity waves called ‘swell’. In this paper, we use large eddy simulations to show that swell-transmitted momentum excites near-inertial waves and drives turbulent mixing that deepens a rotating, stratified, turbulent ocean surface boundary layer. We find that swell-transmitted currents are less effective at producing turbulence and mixing the boundary layer than currents driven by an effective surface stress. Overall, however, the differences between swell-driven and surface-stress-driven boundary layers are relatively minor. In consequence, our results corroborate assumptions made in Earth system models that neglect the vertical structure of swell-transmitted momentum fluxes and instead parameterize all air-sea momentum transfer processes with an effective surface stress.

Corresponding author: Gregory L. Wagner, wagner.greg@gmail.com
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