Field observations of sea spray under Tropical Cyclone Olwyn
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Field observations of sea spray under Tropical Cyclone Olwyn Hongyu Ma 1,2,3,4
&
Alexander V. Babanin 1,3 & Fangli Qiao 2,3,4
Received: 15 June 2020 / Accepted: 6 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Sea spray comprises liquid droplets that cover a broad range of radii, from 0.01 to 1000 μm. For field observations, it is difficult to measure the sea spray size distribution over the full range of radii, particularly as spray production is associated with extreme weather conditions. As a result, differences in magnitude of the sea spray production estimates reach 6 orders. In this study, the sea spray volume flux (SSVF) was measured by laser altimeters under Tropical Cyclone Olwyn in the Indian Ocean. The results show that the SSVF increases gradually with the wind speed and is approximately 2 orders of magnitude larger than the results of two laboratory experiments and existing sea spray generation functions. The SSVF is also influenced by the sea state. When the 1=3 nondimensional significant wave height is factored in a new parameter RB u2* =gH s , the correlation coefficients are improved, increasing to 0.85 and 0.88. Finally, a new parameterization for SSVF generation function is proposed in terms of the nondimensional wave height and windsea Reynolds number RB. Keywords Sea spray . Sea spray volume flux . Tropical cyclone . Waves
1 Introduction As the wind speed increases, sea spray is generated. Two main mechanisms are responsible for the production of such spray: droplets are ejected directly from the sea surface, generally due to wave breaking, or are torn off from the crests of waves due to direct wind action. Three kinds of spray droplets are generated: film droplets, jet droplets and spume droplets (Andreas et al. 1995; Veron 2015). Film droplets are produced when sea surface waves start to break, with air being entrained in the seawater. Bubbles then rise to the surface and burst, and film droplets are generated with radii ranging from 0.01 to 1 μm (Sellegri et al. 2006; de Leeuw et al. Responsible Editor: Jörg-Olaf Wolff * Hongyu Ma [email protected] 1
Department of Infrastructure Engineering, University of Melbourne, Victoria, Australia
2
First Institute of Oceanography, Ministry of Natural Resources, Qingdao, China
3
Laboratory for Regional Oceanography and Numerical Modeling, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China
4
Key Laboratory of Marine Science and Numerical Modeling, Ministry of Natural Resources, Qingdao, China
2011). Subsequently, when the bubble cavity collapses and shoots up a central jet, it becomes unstable and breaks up into several jet droplets with radii of 1–50 μm (Andreas 2002; Lewis and Schwartz 2004). The spume type of droplets is generated by wind’s tearing off sea water directly from wave crests when the wind speed is sufficiently large and has radii between 10 and 1000 μm (Andreas 1992, 2002; Smith et al. 1993; Fairall et al. 1994, 2009; Veron et al. 2012). Clearly, sea spray drop
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