MAPTIP observations of large aerosol in the lowest 10 meters above waves

Abstract

This paper addresses the question of what is the structure of the aerosol concentration profile close to the sea surface during high wind and whitecapping conditions. EO energy must pass through this layer on long horizontal trajectories because of the curvature of the earth. This is also a region of the marine atmosphere where very little is known during high wind conditions. The paper discusses the profile of large aerosol size distribution data obtained from rotorod devices during the MAPTIP experiment. These devices were lowered from an overhang on the Dutch tower, Meetpost Noordwijk, MPN (located about 9 kilometers off the Dutch shore). Altitudes of from 10 meters to just above the wave tops were investigated in calm and high wind conditions. In addition to aerosol size data, relative humidity profiles and other pertinent meteorological measurements were made throughout the MAPTIP experiment and utilized in the analysis. The wind speed dependence of the structure of very large aerosol in the surface layer above the sea is derived from this data. This analysis shows that the turbulence produced by the high wind speed (required to build up the sea state) also mixes the large aerosol in the lowest 10 meters of the atmosphere. This causes any vertical structure in the aerosol spectrum to disappear while the net amount of large aerosol increases non-linearly with the wind speed.