Field validation of wave-wind-dependent sea spray generation functions

Abstract

<p>Recent studies stress the importance of considering sea surface wave characteristics in sea spray generation functions (SSGFs). To this end, the effect of interacting winds and waves on sea spray generation was studied using data collected during the Marine Aerosol Tunnel Experiments (MATE2019) conducted at the OSU-Pytheas large wind-wave tunnel facility at Luminy, Marseille (France) (Study detailed in Bruch et al., in review). A total of 20 wind and wave combinations were tested, with wind speeds between 8 and 20 m s<sup>-1 </sup>combined with pure wind waves and waves generated by a wavemaker, allowing for a range of wave characteristics and wave ages. Similar wind speed profiles and whitecapping behavior between the laboratory and the field suggest that the laboratory is appropriate for the study of sea spray production. The sea spray generation flux was estimated from logarithmic vertical sea spray concentration profiles using a flux-profile method using Monin and Obukhov (1954) theory. Results show that the production of larger droplets at 20-35 µm radius is well correlated with the wave slope variance <S<sup>2</sup>>, whilst the wind friction velocity cubed u<sub>*</sub><sup>3 </sup>performs best over 7-20 µm. Two SSGFs are proposed. <br><br>The original work presented here is an assessment of the validity of the two SSGFs in the field. The two laboratory-derived SSGFs are tested in two numerical models; the stationary Marine Aerosol Concentration Model (MACMod) (used in Laussac et al., 2018), and the non-hydrostatic mesocale atmospheric model Meso-NH (jointly developed by the LA - UMR 5560 - and the CNRM - UMR 3589). The <S<sup>2</sup>> necessary required by both SSGFs is estimated using a wind-dependent formulation (Cox and Munk, 1956) and a spectral spectral model (Elfouhaily et al., 1997). Results show that the numerical simulations offer good results relative to sea spray measurements obtained in the North-West Mediterranean in fetch-limited conditions (Laussac et al., 2018), as well as other existing SSGFs in the literature. These results suggest that wind-wave tunnel facilities present an interesting alternative for determining the sea spray generation flux, especially in high wind speed conditions in which deployment in the field is difficult.</p><p>References :<br><br>Bruch, W., Piazzola, J., Branger, H., van Eijk, A. M. J., Luneau, C., Bourras, D., Tedeschi, G. (In review). Sea Spray Generation Dependence on Wind and Wave Combinations : A Laboratory Study. Submitted in : <em>Boundary Layer Meteorology</em>.</p><p>Cox, C., & Munk, W. (1956). Slopes of the sea surface deduced from photographs of sun glitter. <em>University of California Press</em>. Vol. 6,9,401-488.</p><p>Elfouhaily, T., Chapron, B., Katsaros, K., & Vandemark, D. (1997). A unified directional spectrum for long and short wind driven waves. <em>Journal of Geophysical Research: Oceans</em>, <em>102</em>(C7),15781-15796.<br><br>Monin, A. S., & Obukhov, A. M. (1954). Basic laws of turbulent mixing in the surface layer of the atmosphere. Contrib. Geophys. Inst. Acad. Sci. USSR,151(163),e187.<br><br>Laussac, S., Piazzola, J., Tedeschi, G., Yohia, C., Canepa, E., Rizza, U., & Van Eijk, A. M. J. (2018). Development of a fetch dependent sea-spray source function using aerosol concentration measurements in the North-Western Mediterranean. Atmospheric Environment,193,177-189.</p>

Atmospheric Sea Spray Modeling in the North‐East Atlantic Ocean Using Tunnel‐Derived Generation Functions and the SUMOS Cruise Data Set

“…Nevertheless, some studies suggest that the higher frequency end of the gravity wave spectrum represents a non-negligible and different contribution to the momentum, heat, gas and particle fluxes at the air-sea interface (Jähne & Riemer, 1990;Munk, 2009). The importance of considering different wave scales and complex surface geometry is illustrated in the laboratory study by Bruch et al (2021) where the sea spray generation flux scales best with two formulations, one depending totally, and the other partially, on the upwind component of the multiscale wave-slope variance.…”

“…Both processes are key to sea spray generation, and have a limited dependence on element dimensions. Despite the different wave scales between the laboratory and the field, the SSGFs proposed by Bruch et al (2021) may therefore be valid in real world conditions.…”

“…Measuring jet and spume droplet generation fluxes is a significant challenge in -3-manuscript submitted to JGR: Atmospheres the field. A solution is to take both SSGFs formulated by Bruch et al (2021), and use them in real world conditions. In our study, we integrate the laboratory SSGFs in the mesoscale Meso-NH atmospheric model, and evaluate model performance using a new extensive and original dataset constructed during the SUMOS field campaign in the Bay of Biscay.…”

“…This new nomenclature allows to better distinguish between the two SSGFs presented by Bruch et al (2021).…”

“…We reuse the MATE19 (Bruch et al, 2021) wind and wave data, collected for five U 10 wind speeds ranging 8-20 m s -1 , and four wave-types: one pure wind-wave case, and three monochromatic wave cases generated with a mechanical wavemaker. During MATE19, the wave-slope variance was obtained from differences in the water surface elevation, measured with an array of three wave gauges aligned with the general wind and wave direction, 10 mm apart, with a 256 Hz sampling frequency.…”