Winds near the Surface of Waves: Observations and Modeling

Babanin, Alexander V.; McConochie, Jason; Chalikov, Dmitry

doi:10.1175/jpo-d-17-0009.1

Cited by 23 publications

(22 citation statements)

References 18 publications

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“…When wind blows over the water surface, the surface waves generated by the wind exert wave-coherent perturbations on the wind (Harris, 1966) due to the difference in the pressure distribution before and after wave crests (e.g., Buckley & Veron, 2016). The wave-coherent perturbations merge into turbulence, significantly changing the stress and vectors when the stress is computed by the eddy correlation method (Rieder & Smith, 1998) and invalidating the MOST within the wave boundary layer (Babanin et al, 2018).…”

Section: Methodsmentioning

confidence: 99%

Effects of Swell Waves on Atmospheric Boundary Layer Turbulence: A Low Wind Field Study

Zou

Song

et al. 2019

JGR Oceans

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The effect of swell waves on atmospheric boundary layer turbulence under low winds was explored using data from a fixed platform located in the South China Sea. The wind spectra, cospectra, and Ogive curve measured at a height of 8 m above the mean sea surface provided direct evidence that wind stress was affected by swell waves. To interpret such phenomena, an improved approach was derived based on the fact that the total wind stress was the vector sum of turbulent stress and wave‐coherent stress. Different from the approaches of earlier studies, our approach did not align the turbulent stress with the mean wind speed. The influence of swell waves on the magnitude and direction of the total wind stress was analyzed using our approach. The results showed that the wave‐coherent stress derived from our data accounted for 32% of the total wind stress. The magnitude and angle of the wind stress changed by swell waves depended on the relative angle between the turbulent stress and swell direction.

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Section: Methodsmentioning

confidence: 99%

Effects of Swell Waves on Atmospheric Boundary Layer Turbulence: A Low Wind Field Study

Zou

Song

et al. 2019

JGR Oceans

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“…In these situations, wave-induced momentum is transferred from the ocean to the atmosphere (cf. Grachev and Fairall [6], Babanin et al [19], Högström et al [26]). In counter-swell situations, the wind drags against the waves, i.e., τ 2 < 0, and momentum is extracted from the atmosphere (cf.…”

Section: Methodsmentioning

confidence: 99%

“…where ρ denotes the air density, the brackets denote a time-average mean and i and j represent the longitudinal and lateral unit vectors, respectively. The wave-induced fluctuations are expected to decrease exponentially with height [17][18][19] and the wind stress outside the WBL is thus only supported by the turbulent fluctuations around the mean values of the wind speed components. The deviation of the wind stress direction from the wind direction, i.e., the off-wind angle, is correspondingly determined as…”

Section: Methodsmentioning

confidence: 99%

“…However, this approach might fail to provide accurate surface stress estimates due to advection of vertical momentum flux and consecutive changes in the surface layer wind stress (cf. Mahrt et al [12,13] Babanin et al [19], Hare et al [29], Miller [30]). Revisiting data from several offshore measurement campaigns, Mahrt et al [13] noted that the vertical momentum flux, i.e., the wind stress magnitude, decreases (increases) with height over the open ocean (in coastal areas) due to momentum flux divergence (convergence).…”

Section: Methodsmentioning

confidence: 99%

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Wind Stress in the Coastal Zone: Observations from a Buoy in Southwestern Norway

et al. 2019

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Several studies have focused on the investigation of the wind stress in open ocean conditions where coastal processes were negligible. However, the direction and magnitude of the wind stress vector in coastal areas are still not fully known due to the low number of available measurement datasets. Here, we present new observations of the wind stress magnitude and its deviation from the mean wind direction. The data were recorded from a surface buoy during a five-day measurement campaign in southwestern Norway and cover wind speeds up to 10 m s−1 and significant wave heights up to 3.5 m in a coastal area with a steeply sloping sea floor. The adjustment of the wind stress vector due to changes in the wind and the wave conditions is illustrated and discussed by means of seven sample cases associated with both wind-following swell, cross-swell and counter-swell conditions. For this purpose, the stress vector computed in the sonic anemometer’s orthogonal coordinate system is projected into a non-orthogonal wind-swell coordinate system with its components aligned with: (1) the local wind-generated waves propagating in the wind direction; and (2) the swell wave direction. The wind stress direction was found to deviate from the wind direction by more than 20° for 46% of the recorded wind-following swell and cross-swell cases and for 54% of the counter-swell cases. The wind stress magnitude was observed to approach zero during the counter-swell period, which suggest a decoupling between the sea surface and the atmospheric surface layer. This was further investigated by means of an idealized Large Eddy Simulation results. The results in this study provide additional experimental evidence that the wind stress direction in coastal areas with a steeply sloping sea floor is influenced by the swell waves, the wave age and the wave steepness when the wind blows from undisturbed open ocean directions. For landward wind directions, the influence of the land boundary layer can, possibly in combination with atmospheric stability, adjust the magnitude and direction of the wind stress.

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“…Parametrization of the wind stress is essential for ocean general circulation models and climate models. Although wind stress over the ocean surface has been studied for more than half a century, there are still high uncertainties associated with the determination of wind stress (Babanin et al, 2018;Chen et al, 2019;Jones & Toba, 2001).…”

Section: Introductionmentioning

confidence: 99%

Directional Characteristic of Wind Stress Vector Under Swell‐Dominated Conditions

et al. 2020

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The wind stress vector over the ocean surface is often misaligned with the wind direction; this misalignment in a swell‐dominated regime is not well investigated. Directional characteristic of the wind stress vector under swell‐dominated conditions is analyzed through direct flux observations taken over the coastal region in the northern South China Sea. Observational Ogive curves demonstrate that an additional velocity component induced by a strong swell at wind speeds below 4 m/s can be captured at a height of 17 m away from the sea surface. Our results show that swell can cause a deviation in the wind stress from the wind direction, and the stress vectors mostly reside between the wind direction and the opposite swell direction under low to moderate wind and strong background swell conditions. Further directional analysis indicates that the deviation in the stress vector from the wind vector is mainly governed by the speeds and directions of the wind and swell. With the increase in the wind speed and inverse wave age, this deviation decreases and becomes less scattered; additionally, it increases with the angle between the wind and swell directions, and a linear relation is proposed at wind speeds greater than 6 m/s.

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Winds near the Surface of Waves: Observations and Modeling

Cited by 23 publications

References 18 publications

Effects of Swell Waves on Atmospheric Boundary Layer Turbulence: A Low Wind Field Study

Effects of Swell Waves on Atmospheric Boundary Layer Turbulence: A Low Wind Field Study

Wind Stress in the Coastal Zone: Observations from a Buoy in Southwestern Norway

Directional Characteristic of Wind Stress Vector Under Swell‐Dominated Conditions

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