Spatial inhomogeneities and the spectral behavior of atmospheric aerosol optical depth over the Atlantic Ocean

In this paper the results of investigations into atmospheric aerosol optical depth (AOD) over the Atlantic Ocean are discussed. The data were collected during five shipboard expeditions that took place between 1989 and 1996. Measurements were taken by a 0.37-4-mum multiwavelength sun photometer, specially designed for working conditions on board a ship. The analysis focuses on the spatial variability of atmospheric transparency and the spectral behavior of AOD in different oceanic areas. The genetic zoning of aerosol turbidity takes into account the influence of two factors: the type of continental aerosol and the character of airmass transport that dominates in a given latitudinal zone. The area selection by the genetic zoning method is further confirmed by the results of the "sign'' classification based on the spatial distributions of AOD and the Angstrom parameter. Statistical characteristics for different areas of the Atlantic are given. The mean values of AOD (0.55 mum) range from 0.08 to 0.38 and the mean Angstrom parameters from 0.3 to 1.1. The spectral dependencies of AOD in the extended wavelength range (0.37-4 mum) are represented as the sum of two components related to the contribution of fine and coarse aerosols. It is noted that the largest spatial inhomogeneities of integral atmospheric transparency are caused by the aerosol component, and in most areas the coarse aerosol is a principal contributor to the extinction of radiation.