An improved whitecap timescale for sea spray aerosol production flux modeling using the discrete whitecap method
Callaghan, Adrian H.
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Callaghan, Adrian H. (2013). An improved whitecap timescale for sea spray aerosol production flux modeling using the discrete whitecap method. Journal of Geophysical Research: Atmospheres 118 (17), 9997-10010
The discrete whitecap method (DWM) to model the sea spray aerosol (SSA) production flux explicitly requires a whitecap timescale, which up to now has only considered a whitecap decay timescale, (decay). A reevaluation of the DWM suggests that the whitecap timescale should account for the total whitecap lifetime ((wcap)), which consists of both the formation timescale ((form)) and the decay timescale (timescale definitions are given in the text). Here values of (form) for 552 oceanic whitecaps measured at the Martha's Vineyard Coastal Observatory on the east coast of the USA are presented, and added to the corresponding values of (decay) to form 552 whitecap timescales. For the majority of whitecaps, (form) makes up about 20-25% of (wcap), but this can be as large as 70% depending on the value of (decay). Furthermore, an area-weighted mean whitecap timescale for use in the DWM ((DWM)) is defined that encompasses the variable nature of individual whitecap lifetimes within a given time period, and is calculated to be 5.3s for this entire data set. This value is combined with previously published whitecap coverage parameterizations and estimates of SSA particle production per whitecap area to form a size-resolved SSA production flux parameterization (dF(r(80))/dlog(10)r(80)). This parameterization yields integrated sea-salt mass fluxes that are largely within the range of uncertainty of recent measurements over the size range 0.029 mu m&lt;r(80)&lt;0.580 mu m. Physical factors controlling whitecap lifetime such as bubble plume lifetime and surfactant stabilization are discussed in the context of SSA production from whitecaps.