Calendar Event Details
AEROCENTER: Adrian H. Callaghan
Affiliation: Scripps Institution of Oceanography
Event Date: Tuesday, May 13, 2014
Location: G133
Time: 11:00 AM
An Improved Whitecap Timescale for Sea Spray Aerosol Production Flux Modeling with the Discrete Whitecap Method
Air-entraining breaking waves at the air-sea interface produce submerged plumes of bubble that rise to the surface and form visible whitecap foam. As bubbles burst and the foam decays, tiny sea spray aerosol (SSA) particles with a size range of 10 nm to several millimeters are ejected into the atmosphere where they reside on timescales of seconds to days depending on their size and primary removal mechanism. These particles affect the number and size of droplets in marine clouds, and directly scatter electromagnetic radiation over much of the world’s oceans. Accurate knowledge of marine aerosol production flux is therefore important to represent how SSA particles directly and in-directly affect the Earth’s radiation budget and climate.
E. C. Monahan and colleagues pioneered the use of the discrete whitecap method (DWM) to model the size-resolved number production flux of sea spray aerosol (SSA) particles from the ocean surface. The DWM combines laboratory measurements of size-resolved SSA particles from simulated whitecaps (dE/dr) with estimates of the instantaneous oceanic whitecap coverage (W) and a characteristic whitecap decay timescale (τdecay) to predict the number of size-resolved SSA particles per unit sea surface area per second (dF/dr). The DWM has been effectively incorporated into several chemical transport models and global climate models to quantify the role of marine derived aerosols in atmospheric forcing.
In this seminar I will discuss how detailed knowledge of the evolution of individual whitecaps can improve our understanding of whitecap coverage and whitecap timescales, with important consequences for the DWM. In particular, I will present results from recent field and laboratory campaigns that document the variability in the sizes and lifetimes of individual whitecaps and elucidate what physical and chemical factors control the lifetime of individual whitecaps. These results highlight the importance of choosing the correct whitecap timescale in the DWM, and a new whitecap timescale termed the effective whitecap lifetime is derived which replaces the whitecap decay timescale that is currently implemented in most formulations of the DWM. Finally, a revised DWM sea-spray production flux parameterization is proposed which yields integrated sea-salt mass fluxes that are largely within the range of uncertainty of recent field measurements over the size range 0.029 μm < r80 < 0.580 μm.