Wind Turbulence over Misaligned Surface Waves and Air–Sea Momentum Flux. Part I: Waves Following and Opposing Wind
- 1 January 2022
- journal article
- research article
- Published by American Meteorological Society in Journal of Physical Oceanography
- Vol. 52 (1), 119-139
- https://doi.org/10.1175/jpo-d-21-0043.1
Abstract
Air-sea momentum and scalar fluxes are strongly influenced by the coupling dynamics between turbulent winds and a spectrum of waves. Because direct field observations are difficult, particularly in high winds, many modeling and laboratory studies have aimed to elucidate the impacts of the sea state and other surface wave features on momentum and energy fluxes between wind and waves as well as on the mean wind profile and drag coefficient. Opposing wind is common under transient winds, for example under tropical cyclones, but few studies have examined its impacts on air-sea fluxes. In this study, we employ a large eddy simulation for wind blowing over steep sinusoidal waves of varying phase speeds, both following and opposing wind, to investigate impacts on the mean wind profile, drag coefficient, and wave growth/decay rates. The airflow dynamics and impacts rapidly change as the wave age increases for waves following wind. However, there is a rather smooth transition from the slowest waves following wind to the fastest waves opposing wind, with gradual enhancement of a flow perturbation identified by a strong vorticity layer detached from the crest despite the absence of apparent airflow separation. The vorticity layer appears to increase the effective surface roughness and wave form drag (wave attenuation rate) substantially for faster waves opposing wind. Air-sea momentum and scalar fluxes are strongly influenced by the coupling dynamics between turbulent winds and a spectrum of waves. Because direct field observations are difficult, particularly in high winds, many modeling and laboratory studies have aimed to elucidate the impacts of the sea state and other surface wave features on momentum and energy fluxes between wind and waves as well as on the mean wind profile and drag coefficient. Opposing wind is common under transient winds, for example under tropical cyclones, but few studies have examined its impacts on air-sea fluxes. In this study, we employ a large eddy simulation for wind blowing over steep sinusoidal waves of varying phase speeds, both following and opposing wind, to investigate impacts on the mean wind profile, drag coefficient, and wave growth/decay rates. The airflow dynamics and impacts rapidly change as the wave age increases for waves following wind. However, there is a rather smooth transition from the slowest waves following wind to the fastest waves opposing wind, with gradual enhancement of a flow perturbation identified by a strong vorticity layer detached from the crest despite the absence of apparent airflow separation. The vorticity layer appears to increase the effective surface roughness and wave form drag (wave attenuation rate) substantially for faster waves opposing wind.Keywords
Funding Information
- National Science Foundation (1458984)
This publication has 95 references indexed in Scilit:
- Impact of Ocean Spray on the Dynamics of the Marine Atmospheric Boundary LayerBoundary-Layer Meteorology, 2011
- Coupled Numerical Modelling of Wind and Waves and the Theory of the Wave Boundary LayerBoundary-Layer Meteorology, 2010
- Air Flow Structure Over Short-gravity Breaking Water WavesBoundary-Layer Meteorology, 2007
- Swell and Slanting-Fetch Effects on Wind Wave GrowthJournal of Physical Oceanography, 2007
- On the limiting aerodynamic roughness of the ocean in very strong windsGeophysical Research Letters, 2004
- Wind Stress Vector over Ocean WavesJournal of Physical Oceanography, 2003
- Coupled dynamics of short waves and the airflow over long surface wavesPublished by American Geophysical Union (AGU) ,2002
- Coupled sea surface‐atmosphere model: 1. Wind over waves couplingPublished by American Geophysical Union (AGU) ,1999
- Separation Control: ReviewJournal of Fluids Engineering, 1991
- Turbulent airflow over water waves-a numerical studyJournal of Fluid Mechanics, 1984