Evaluating Primary Marine Aerosol Production and Atmospheric Roll Structures in Hawaii’s Natural Oceanic Wind Tunnel

Topography-induced steady-state accelerated wind flow in the Alenuihaha Channel between the islands of Hawaii and Maui provides about 100 km of fetch with winds that can nearly double over trade wind speed. Here ship- and aircraft-based observations of meteorological parameters and aerosols in Hawaii’s orographic natural “wind tunnel” are used for the study of sea salt aerosol (SSA) production, evolution, and related optical effects under clean oceanic conditions. There are certain advantages of channel measurements, such as a broad and uniform upstream area usually filled with background aerosol, stationary flow, and known fetch, but also some difficulties, like vigorous entrainment and persistent presence of organized structures (rolls). It is found that marine boundary layer (MBL) rolls are a common occurrence near the Hawaiian Islands even when cloud streets are not visible in satellite imagery. The presence of rolls tends to enhance the variability of ambient aerosol concentration and probably affects production of primary sea salt aerosol and entrainment from above. The possibility of channel measurements of the size-dependent flux of SSA is explored using a concentration buildup method as surface wind speeds range from 7 to 11 m s−1. Production of SSA particles with dry diameter as small as 0.18 μm was observed. General agreement with reported SSA fluxes was found.