Sea-salt optical properties and GCM forcing at solar wavelengths |
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| Authors: | Steven Dobbie Jiangnan Li Richard Harvey Petr Chýlek |
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| Institution: | a Institute for Atmospheric Science, School of the Environment, University of Leeds, Leeds LS2 9JT, UK;b Canadian Centre For Climate Modeling and Analysis, Atmospheric Environment Service, University of Victoria, Victoria, British Columbia, Canada V8P 2Y2;c Atmospheric Science Program, Departments of Physics and Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5 |
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| Abstract: | The single-scattering optical properties of sea-salt solution particles are parameterised as functions of relative humidity for various dry size distributions at solar wavelengths. The accuracy of the parameterisation is typically within 10% as compared to exact Mie calculations. In addition to the optical properties, the growth of the droplet mass ratio and the effective radius of the size distribution are also parameterised in terms of the relative humidity. Two-band models are presented: a four-band model for use in GCMs for climate studies and a 23-band model for use in higher spectral resolution models. The parameterisation is implemented in the Canadian General Circulation Model GCMIII, and an estimate of the first-order globally and yearly averaged solar direct radiative forcing due to sea-salt is estimated to be −0.15 W/m2 (cooling). The northern hemisphere forcing is estimated to be −0.11 W/m2 and the southern hemisphere is −0.19 W/m2. The monthly trends in the forcing for the two hemispheres are presented and discussed. The sensitivity of the forcing to the treatment of the growth of aerosols in the hysteresis region, where aerosol particles are either dry or supersaturated, is investigated along with other sensitivities. |
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| Keywords: | Forcing Sea-salt Aerosols GCM |
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