Breaking waves and near-surface sea spray aerosol dependence on changing winds: Wave breaking efficiency and bubble-related air-sea interaction processes

Hwang, Paul A.; Savelyev, Ivan; Anguelova, Magdalena D.

doi:10.1088/1755-1315/35/1/012004

Cited by 8 publications

(5 citation statements)

References 31 publications

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“…The pressure signal was sampled at 10 Hz. For YDs 119–120, significant wave heights from 3 to ∼5 m were measured [ Anguelova et al ., ] with the spectral peak periods of the wind‐sea and swell components ranging from ∼8 to 13 s [ Hwang et al ., ] and wind‐sea peak phase speed ranging from 8 to ∼15 m s −1 . The environmental conditions during BREWEX were seawater temperature of 13°C in the mixed layer (0–10 m), nearly neutral atmospheric stability, and salinity of 32.6 practical salinity unit (psu) [ Savelyev et al ., ].…”

Section: Instrumentationmentioning

confidence: 99%

Whitecap lifetime stages from infrared imagery with implications for microwave radiometric measurements of whitecap fraction

Potter¹,

Smith²,

Snow

et al. 2015

JGR Oceans

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Quantifying active and residual whitecap fractions separately can improve parameterizations of air‐sea fluxes associated with breaking waves. We use data from a multi‐instrumental field campaign on Floating Instrument Platform (FLIP) to simultaneously capture the signatures of active and residual whitecaps at visible, infrared (IR), and microwave wavelengths using, respectively, video camera, mid‐IR camera, and a radiometer at 10 GHz. We present results from processing and analyzing IR images and correlating this information with radiometric time series of brightness temperature at horizontal and vertical polarizations TBH and TBV. The results provide evidence that breaking crests and decaying foam appear in mid‐IR as bright and dark pixels clearly distinguishing active from residual whitecaps. We quantify the durations of whitecap lifetime stages from the IR images and identify their corresponding signatures in TB time series. Results show that TBH and TBV vary in phase during the active and in antiphase during the residual whitecap stages. A methodology to distinguish active and residual whitecaps in radiometric time series without a priori IR information has been developed and verified with corresponding IR and video images. The method uses the degree of polarization P (the ratio between the sum and difference of TBV and TBH) to capture whitecaps as prominent spikes. The maximum and zero‐crossing of the first derivative of P serve to identify the presence of active whitecaps, while the minimum of dP marks the transition from active to residual whitecap stage. The findings have implications for radiometric measurements of active and total whitecap fractions.

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Section: Instrumentationmentioning

confidence: 99%

Whitecap lifetime stages from infrared imagery with implications for microwave radiometric measurements of whitecap fraction

Potter¹,

Smith²,

Snow

et al. 2015

JGR Oceans

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Section: Influence Of Other Parametersmentioning

confidence: 99%

Ocean bubbles under high wind conditions – Part 1: Bubble distribution and development

et al. 2022

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Abstract. The bubbles generated by breaking waves are of considerable scientific interest due to their influence on air–sea gas transfer, aerosol production, and upper ocean optics and acoustics. However, a detailed understanding of the processes creating deeper bubble plumes (extending 2–10 m below the ocean surface) and their significance for air–sea gas exchange is still lacking. Here, we present bubble measurements from the HiWinGS expedition in the North Atlantic in 2013, collected during several storms with wind speeds of 10–27 m s−1. A suite of instruments was used to measure bubbles from a self-orienting free-floating spar buoy: a specialised bubble camera, acoustical resonators, and an upward-pointing sonar. The focus in this paper is on bubble void fractions and plume structure. The results are consistent with the presence of a heterogeneous shallow bubble layer occupying the top 1–2 m of the ocean, which is regularly replenished by breaking waves, and deeper plumes which are only formed from the shallow layer at the convergence zones of Langmuir circulation. These advection events are not directly connected to surface breaking. The void fraction distributions at 2 m depth show a sharp cut-off at a void fraction of 10−4.5 even in the highest winds, implying the existence of mechanisms limiting the void fractions close to the surface. Below wind speeds of 16 m s−1 or a wind-wave Reynolds number of RHw=2×106, the probability distribution of void fraction at 2 m depth is very similar in all conditions but increases significantly above either threshold. Void fractions are significantly different during periods of rising and falling winds, but there is no distinction with wave age. There is a complex near-surface flow structure due to Langmuir circulation, Stokes drift, and wind-induced current shear which influences the spatial distribution of bubbles within the top few metres. We do not see evidence for slow bubble dissolution as bubbles are carried downwards, implying that collapse is the more likely termination process. We conclude that the shallow and deeper bubble layers need to be studied simultaneously to link them to the 3D flow patterns in the top few metres of the ocean. Many open questions remain about the extent to which deep bubble plumes contribute to air–sea gas transfer. A companion paper (Czerski et al., 2022) addresses the observed bubble size distributions and the processes responsible for them.

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“…Other parameters reported to affect bubble formation, movement, and lifetime include phytoplankton presence (Kuhnhenn-Dauben et al, 2008), surface heat flux, upper ocean stratification (Vagle et al, 2012), whether winds are rising or falling (Hwang et al, 2016), and wind-wave Reynolds number (Salisbury et al, 2013;Toba et al, 2006;Scanlon and Ward, 2016;Brumer et al, 2017a). This wide range of potential influences and lack of field data complicates the current efforts to improve parameterisations of ocean processes, a necessary step for improving weather and climate models, and to predict the biogeochemical consequences of our changing climate (Talley et al, 2016).…”

Section: Influence Of Other Parametersmentioning

confidence: 99%

Ocean bubbles under high wind conditions. Part 1: Bubble distribution and development

Czerski

Brooks

Gunn

et al. 2021

Preprint

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Abstract. The bubbles generated by breaking waves are of considerable scientific interest due to their influence on air-sea gas transfer, aerosol production, and upper ocean optics and acoustics. However, a detailed understanding of the processes creating deeper bubble plumes (extending 2–10 metres below the ocean surface) and their significance for air-sea gas exchange is still lacking. Here, we present bubble measurements from the HiWinGS expedition in the North Atlantic in 2013, collected during several storms with wind speeds of 10–27 m s−1. A suite of instruments was used to measure bubbles from a self-orienting free-floating spar buoy: a specialised bubble camera, acoustical resonators, and an upward-pointing sonar. The focus in this paper is on bubble void fractions and plume structure. The results are consistent with the presence of a heterogeneous shallow bubble layer occupying the top 1–2 m of the ocean which is regularly replenished by breaking waves, and deeper plumes which are only formed from the shallow layer at the convergence zones of Langmuir circulation. These advection events are not directly connected to surface breaking. The void fraction distributions at 2 m depth show a sharp cut-off at a void fraction of 10−4.5 even in the highest winds, implying the existence of mechanisms limiting the void fractions close to the surface. Below wind speeds of 16 m s−1 or RHw = 2 × 106, the probability distribution of void fraction at 2 m depth is very similar in all conditions, but increases significantly above either threshold. Void fractions are significantly different during periods of rising and falling winds, but there is no distinction with wave age. There is a complex near-surface flow structure due to Langmuir circulation, Stokes drift, and wind-induced current shear which influences the spatial distribution of bubbles within the top few metres. We do not see evidence for slow bubble dissolution as bubbles are carried downwards, implying that collapse is the more likely termination process. We conclude that the shallow and deeper bubble layers need to be studied simultaneously to link them to the 3D flow patterns in the top few metres of the ocean. Many open questions remain about the extent to which deep bubble plumes contribute to air-sea gas transfer. A companion paper (Czerski, 2021) addresses the observed bubble size distributions and the processes responsible for them.

show abstract

Breaking waves and near-surface sea spray aerosol dependence on changing winds: Wave breaking efficiency and bubble-related air-sea interaction processes

Cited by 8 publications

References 31 publications

Whitecap lifetime stages from infrared imagery with implications for microwave radiometric measurements of whitecap fraction

Whitecap lifetime stages from infrared imagery with implications for microwave radiometric measurements of whitecap fraction

Ocean bubbles under high wind conditions – Part 1: Bubble distribution and development

Ocean bubbles under high wind conditions. Part 1: Bubble distribution and development

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