Spray Generation by a Plunging Breaker

Abstract

An experimental investigation of droplet generation by a plunging breaking wave is presented. In this work, simultaneous measurements of the wave crest profile evolution and of droplets ranging in radius down to 50 μm for a mechanically generated plunging breaker during many repeated breaking events in freshwater are performed. We find three distinct time zones of droplet production, first when the jet impacts the free surface upstream of the wave crest, second when the large air bubbles entrapped by the plunging jet impact reach the free surface and burst, and third when smaller bubbles burst upon reaching the free surface later in the breaking process. These subprocesses account for 22%, 44%, and 34%, respectively, of the average of 653 droplets produced per breaking event. The probability distributions of the ranges of large and small droplet radii are well represented by power law functions that intersect at a radius of 418 μm.

Statistics of Jet Drop Production

“…We comment that film drops are also important in this range and in the data set from Prather et al (2013) but that precise separation between the two processes will depend on the efficiency of the ejection, which might require direct measurements of the surface dynamics. Our distribution is also in good agreement with the data from Erinin et al (2019), but we note that due to different normalizations, only the shape and range of droplets can be discussed.…”

“…We convert the dry-aerosol diameter into liquid droplet radius by considering the conversion factor   80% 2 2 (Lewis & Schwartz, 2004;Tang et al, 1997;Veron, 2015), and keep the absolute count per unit bin size per unit volume from Prather et al (2013) and Quinn et al (2015). Erinin et al (2019) measured the size distribution of liquid drops from 50 μm to 1 mm, resulting from a breaking wave, and separated their data into stage I at early time, which corresponds to spume drops generated at impact, and stage II at later times which coincides with the bubble plume rising and bursting at the surface. While Erinin et al (2019) do not report bubble size distribution data, the breaker is obtained by linear focusing in a similar way as Deane and Stokes (2002) and it is reasonable to assume that the bubble size distribution should be comparable.…”

Examination of the ocean as a source for atmospheric microplastics

“…Every year approximately 6700-7400Tg of sea salt aerosols (SSA) and organic matter from a few nanometres up to~20 μm are produced by wave/wind/interaction which are then transported into the atmosphere through convective updrafts [17,18]. Under normal conditions micro and nano size salt particles are ejected from the sea when breaking waves cause bubbles of trapped air to rise to the surface and burst [19] ( Fig 1A). The bursting of the unsupported surface of the bubble leaves nano sized particles expelled and suspended in the air available for wind transport [20,21].…”

Collective bursting of free-surface bubbles, and the role of surface contamination

“…Classic sea spray generation functions depend on meteorological parameters, primarily the wind speed (Fairall, Kepert & Holland 1994;Lewis & Schwartz 2004), but significant scatter remains in current formulations, in part due to the large range of scales involved (de Leeuw et al 2011;Veron 2015). Sea spray generation is related to surface breaking waves, either directly during wave impact and atomization by wind shear (Veron et al 2012;Erinin et al 2019), or through bubble bursting following air entrainment by breaking (Deike, Melville & Popinet 2016;Deike, Lenain & Melville 2017;Deike & Melville 2018) so that the sea state modulates the droplet production , together with the precise ocean water temperature and composition (salinity, biological activity, etc.) which will impact interfacial phenomena (Wang et al 2017;Frossard et al 2019).…”