9.1 Sea Salt Aerosols along Orographic Coastlines

Wednesday, 15 July 2020: 3:25 PM
Virtual Meeting Room
Alison D. Nugent, Univ. of Hawaii at Mānoa, Honolulu, HI; and C. Taing, K. Ackerman, and J. B. Jensen

Mountains line coastal regions across the world, and waves crash along their shorelines. Sea salt aerosols (SSA) are lofted into the air from these breaking waves, and are lifted into the orographic clouds. Previous studies have shown that cloud droplets grown on SSA act as giant cloud condensation nuclei (GCCN), growing much more rapidly than droplets composed of pure water, likely enhancing the rainfall process. But exactly how much salt is lofting into the atmosphere? Model parameterizations for sea salt emissions from the open ocean depend primarily on wind speed and white capping. Do these models work well for coastlines? Quantifying the size and number concentration of SSA, as well as the forcing responsible, is essential to understanding their influence in coastal regions.

We use the miniature-giant nucleus impactor (mini-GNI) to collect deliquesced salt particles which impact onto polycarbonate slides exposed to the free airstream. These slides are analyzed in a humidified environment under a microscope, quantifying the SSA sizes and concentrations present. We use the mini-GNI to sample on the island of Oahu with a kite platform, to observe at multiple altitudes simultaneously (surface to 800 m), and with a drone platform, to observe from the shoreline to beyond the reef (shoreline, inner reef crest, outer reef crest). We find that SSA concentrations have a strong relationship to wave height in our coastal environment, and that SSA are well mixed in the lowest 500 m but begin to stratify above that level. We find that SSA from wave breaking on reef crests and coastal regions far exceeds the open ocean areas and should be accounted for.
Ultimately, our goals include the quantification of the SSA size and number in the atmosphere, an understanding of the emission drivers, and the impacts to orographic rainfall.
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