The Influence of Swell on the Atmospheric Boundary Layer under Nonneutral Conditions

Zou, Zhongshui; Zhao, Dongliang; Zhang, Jun A.; Li, Shuiqing; Cheng, Yinhe; Lv, Haibin; Ma, Xin

doi:10.1175/jpo-d-17-0195.1

Cited by 20 publications

(9 citation statements)

References 46 publications

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“…Under swell conditions, however, field measurements (Högström et al, ; Högström et al, ; Smedman et al, ) show that swell waves can exert a singular point in the wind profile, which cannot be modeled within the framework of the traditional MOST. The invalid MOST was further confirmed by direct numerical simulation (Kihara et al, ; Sullivan et al, ), large‐eddy simulation (Jiang et al, ; Nilsson et al, ; Sullivan et al, and Sullivan et al, ), and simplified theoretical models (Hanley & Belcher, ; Semedo et al, ; Song et al, and Zou et al, ).…”

Section: Introductionmentioning

confidence: 90%

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: Introductionmentioning

confidence: 90%

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 wave‐induced stress can be calculated through the wave spectrum, which has been widely used to correct the turbulent stress to be consistent with the actual total stress (Babanin et al, 2018; Chen et al, 2019; Zou et al, 2018). Here, we apply the same method into our observations and find that this correction is feasible (Figure S2).…”

Section: Resultsmentioning

confidence: 99%

“…However, the actual height of the critical layer with the swell impact is difficult to be determined. Previous MABL models were generally developed based on the assumption of constant flux layer to simulate vertical wind profiles and wave-driven wind speed under swell conditions (Semedo et al, 2009;Zou et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…However, the actual height of the critical layer with the swell impact is difficult to be determined. Previous MABL models were generally developed based on the assumption of constant flux layer to simulate vertical wind profiles and wave‐driven wind speed under swell conditions (Semedo et al, 2009; Zou et al, 2018). The assumption of constant flux layer is that the total wind stress τ does not vary with height z in the near‐surface MABL:

\partial τ / \partial z = 0

here,

τ = τ_{turb} + τ_{wave} + τ_{visc} = u_{*}^{2}

.…”

Section: Introductionmentioning

confidence: 99%

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Swell Modulation on Wind Stress in the Constant Flux Layer

Chen

Zhang

et al. 2020

Geophysical Research Letters

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The impact of swell on wind stress is investigated through direct three-layer flux measurements taken by a fixed tower in the marine atmospheric boundary layer. Observations confirm that the assumption of constant momentum flux layer is valid under swell-dominated conditions around the reference height of 10 m. The swell can modulate the total wind stress to be less than the turbulent stress derived from the first-order closure method, and the extent of this modulation decreases with height. The critical layer that represents the top of the layer affected by stronger swells is estimated to reach 45-m altitude, and the depth of this layer decreases as the swells weaken and the wind speed increases. Furthermore, a simple swell correction scheme for the total stress calculation is developed, showing good performance against observations. Plain Language Summary The swell plays a vital role in the modulation of wind stress and has a remarkable influence on the structure of the marine atmospheric boundary layer (MABL). Investigation of the swell impact on wind stress is thus important for understanding the complex air-sea interaction and for improving ocean-atmosphere coupled models. The study investigates the effect of swell on the wind stress in the surface layer using direct flux and wave observations. For the first time, observations confirm that the surface layer satisfies the constant flux layer assumption under swell conditions, and the degree of swell influence on the wind stress decreases with height. The critical height scale that represents the top of layer that has the swell effect may be larger than 45 m, which depends on the wind speed and wave age. A simple scheme is developed to consider the swell effect in total flux calculation. The predicted wind stress by this scheme shows a good agreement with the measured wind stress.

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“…Unlike the land surface, the ocean surface is mobile; therefore, surface waves, have a crucial impact on the stress vector (Chen et al, 2019;Pan et al, 2005;Zou et al, 2018Zou et al, , 2019. Giovanangeli et al (1994) showed that the deviation of wind stress from the wind direction depends on the swell direction and steepness based on the wind-wave tunnel measurements.…”

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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The Influence of Swell on the Atmospheric Boundary Layer under Nonneutral Conditions

Cited by 20 publications

References 46 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

Swell Modulation on Wind Stress in the Constant Flux Layer

Directional Characteristic of Wind Stress Vector Under Swell‐Dominated Conditions

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