Thursday, 13 February 2003
The contribution of coastal aerosol from breaking waves to visible and IR light–extinction over a 10km optical path during RED
The Rough Evaporation Duct (RED) experiment was carried out off the NE coast of Oahu, Hawaii in August-September of 2001. A 10km electro-optic (EO) path between the R/V FLIP anchored off the coast and a receiver on the coast passed over a near shore region of frequent breaking waves about 500m in front of the detector. Marine aerosol produced from these breaking waves varied in intensity of production and in the degree to which it intercepted the EO path depending upon environmental factors including wind direction. Because the EO path was designed to pass only about 2m above the surface these aerosol usually intercepted the EO path over some distance. Our UH aerosol research van (UHV) was located about 400m toward FLIP from the EO detector and about 100m north of the EO path. It was located at a coastal section with only close near shore breaking waves that seldom experienced conditions that allowed them to enter our 12m high UHV inlet. This meant the UHV sampled open-ocean aerosol unless more southerly winds brought aerosol from the breaking wave region upwind of the EO detector. The latter cases had far higher extinction values, allowing us to distinguish the influence of these waves upon the RED EO path extinction. Our UHV measurements included the aerosol size distribution from 10nm to over 10um in conjunction with optical measurements including aerosol light scattering and light absorption. Thermal heating of the aerosol to 300C was also used to remove volatile components and characterize the refractory sea-salt component. The sample mast was also removed for a period to get the near surface size-distributions at 3m altitude and concurrent extinction data for interpretation of similar values for the near surface EO path. Analysis of the coastal geometry and the wind speeds were then used to estimate the impact of both the open ocean aerosol and the contributions of aerosol from breaking waves upon the 10km EO signal.