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  • Author or Editor: Magdalena D. Anguelova x
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Magdalena D. Anguelova
Paul A. Hwang


Active and total whitecap fractions quantify the spatial extent of oceanic whitecaps in different lifetime stages. Total whitecap fraction W includes both the dynamic foam patches of the initial breaking and the static foam patches during whitecap decay. Dynamic air–sea processes in the upper ocean are best parameterized in terms of active whitecap fraction W A associated with actively breaking crests. The conventional intensity threshold approach used to extract W A from photographs is subjective, which contributes to the wide spread of W A data. A novel approach of obtaining W A from energy dissipation rate ε is proposed. An expression for W A is derived in terms of energy dissipation rate W A (ε) on the basis of the Phillips concept of breaking crest length distribution. This approach allows more objective determination of W A using the breaker kinematic and dynamic properties yet avoids the use of measuring breaking crest distribution from photographs. The feasibility of using W A (ε) is demonstrated with one possible implementation using buoy data and a parametric model for the energy dissipation rate. Results from W A (ε) are compared to W A from photographic data. Sensitivity analysis quantifies variations in W A estimates caused by different parameter choices in the W A (ε) expression. The breaking strength parameter b has the greatest influence on the W A (ε) estimates, followed by the breaker minimal speed and bubble persistence time. The merits and caveats of the novel approach, possible improvements, and implications for using the W A (ε) expression to extract W A from satellite-based radiometric measurements of W are discussed.

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Primary Marine Aerosol Fluxes

Progress and Priorities

Ian M. Brooks
Edgar L Andreas
Gordon McFiggans
Magdalena D. Anguelova
, and
Colin O'Dowd

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