Sea spray can contribute significantly to the exchanges of heat and momentum across the air–sea interface. However, while critical, sea spray physics are typically not included in operational atmospheric and oceanic models due to large uncertainties in their parameterizations. In large part, this is because of the scarcity of in-situ sea spray observations which prevent rigorous validation of existing sea spray models. Moreover, while sea spray is critically produced through the fundamental interactions between wind and waves, traditionally, sea spray models are parameterized in terms of wind properties only. In this study, we present novel in-situ observations of sea spray derived from a laser altimeter through the adoption of the Beer–Lambert law. Observations of sea spray cover a broad range of wind and wave properties and are used to develop a wind–wave-dependent sea spray volume flux model. Improved performance of the model is observed when wave properties are included, in contrast to a parameterization based on wind properties alone. The novel in-situ sea spray observations and the predictive model derived here are consistent with the classic spray model in both trend and magnitude. Our model and novel observations provide opportunities to improve the prediction of air–sea fluxes in operational weather forecasting models.

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.

Surfactant layers with viscoelastic properties floating on the water surface dampen short gravity-capillary waves. Taking advantage of the known virtue of fish oil to still angry seas, a laboratory study has been made to analyse wind-wave generation and the interaction between wind waves, paddle waves, and airflow. This was done in a tank containing a thin fish-oil film uniformly spread on the water surface. The research was aimed, on the one hand, at quantifying for the first time the effectiveness of this surfactant at impeding the generation of wind waves and, on the other, at using the derived conditions to disentangle relevant mechanisms involved in the air–sea interaction. In particular, our main interest concerned the processes acting on the wind stress and on the wave growth. With oil on the water surface, we have found that in the wind-only condition (no paddle waves) the wave field does not grow from the rest condition. This equilibrium is altered by irregular paddle (long) waves, the generation and evolution of short waves (in clean water and with oil) being modified by their interaction with the orbital velocity of the long waves and their effect on the airflow. Paddle waves do grow under the action of wind, the amount being similar in clean and oily water conditions, a fact we ascribe to the similar distortion of the wind vertical profile in the two cases. We have also verified that the wind-supported stress on the oily water surface was able to generate a surface current, whose magnitude turns out to be comparable to the one in clean water. We stress the benefits of experiments with surfactants to explore in detail the physics at, and the exchanges across, the wavy and non-wavy air–water interface.

By using an acoustic Doppler velocimeter mounted on the seabed of the continental shelf of the northern South China Sea, high frequency velocity fluctuations were measured for 4.5 days. The turbulent kinetic energy dissipation rate was estimated. During the observation, the strong ocean response to Typhoon Rammasun was recorded to compare the turbulent characteristics before and during the typhoon. The results show that the turbulence near the seabed is mainly generated by the tidal current shear and exhibits a quarter diurnal variation during the period before the typhoon. During the typhoon period, the dissipation rate ε dramatically increased from 1 × 10⁻⁶ to 1 × 10⁻² m² s⁻³ within a short time, and the significant wave height and the surface wave orbital velocity showed the same tendency. This finding suggests that the turbulence is dominantly generated by the surface waves near the seabed.

Results of measurements of the drift currents induced by waves and wind at the wavy water surface are presented. The measurements were executed by means of surface floats in a large tank with the dimensions of 32.5x1x2 m3. Three cases were studied: (i) regular (narrow-band) mechanical waves; (ii) irregular (wide-band) mechanical waves; and (iii) wind waves.The measured surface-drift currents induced by mechanical waves, Ud, are compared with the Stokes drift at the surface, USt, estimated by the well-known formula with the integral over a wave spectrum. In this case, it was found that ratio Ud / USt is varying in the range 0.5 – 0.93 and slightly growing with the decrease of wave steepness, having no visible dependence on the breaking intensity. These estimations are used to separate the wind-induced drift current, Udw, from the total drift at the presence of wind.In the case of wind waves, the wind-induced part of the surface drift, Udw, is compared with the friction velocity, u*. In our measurements, the ratio Udw / u* varies systematically in the range 0.65 – 1.2. Taking into account the percentage of wave breaking, Br, the wave age, A, and the wave steepness, Ϭ = akp, it was found the parameterization:  Udw = (Br + Ϭ A) u*, which corresponds to the observations with the mean error less than 10%. For the first time, this ratio provides the dependence of the surface wind drift on the surface wave parameters.