Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 8 2 2008 10.5194/acpd-8-5813-2008 http://www.atmos-chem-phys-discuss.net/8/5813/2008/ http://www.atmos-chem-phys-discuss.net/8/5813/2008/acpd-8-5813-2008.html http://www.atmos-chem-phys-discuss.net/8/5813/2008/acpd-8-5813-2008.pdf 5813 5845 2008-03-19 Parameterization of sea-salt optical properties and physics of the associated radiative forcing J. Li jiangnan.li@ec.gc.ca X. Ma K. von Salzen S. Dobbie Canadian Centre For Climate Modelling and Analysis, Science and Technology Branch, Environment Canada, University of Victoria, Victoria, British Columbia, Canada Inst. for Atmospheric Science, School of Earth and Environment, Univ. of Leeds, Leeds, UK The optical properties of sea-salt aerosol have been parameterized at solar and longwave wavelengths. The optical properties were parameterized in a simple functional form in terms of the ambient relative humidity based on Mie optical property calculations. The proposed parameterization is tested relative to Mie calculations and is found to be accurate to within a few percent. In the parameterization, the effects of the size distribution on the optical properties are accounted for in terms of effective radius of the sea-salt size distribution. This parameterization differs from previous works by being formulated directly with the wet sea-salt size distribution (and compared to AERONET results) and, to our knowledge, this is the first published sea-salt parameterization to provide a parameterization for both solar and longwave wavelengths. We have used this parameterization in a set of idealized 1-D radiative transfer calculations to investigate the sensitivity of various attributes of sea-salt forcing, such as dependence with sea-salt column loading, effective variance, solar angle, and surface albedo. From these sensitivity tests, it is found that sea-salt forcings for both solar and longwave spectra are linearly related to the sea-salt loading for realistic values of loadings. The radiative forcing results illustrate that the shortwave forcing is an order of magnitude greater than the longwave forcing results and opposite in sign, for various loadings. Studies of the sensitivity of forcing results to variations in effective variance show there to be minimal variation; therefore, only one value of effective variance is used in the parameterization. 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