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RESEARCH PRODUCT

A Fast Solar Radiation Transfer Code for Application in Climate Models

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A method is presented for the calculation of solar heating rates in turbid and cloudy atmospheres. In contrast to other typical two-stream procedures, the system of differential equations describing the radiative transfer is decoupled through the application of a series expansion of the flux densities resulting in a single analytical expression for each flux. The present method (PM) yields a solution for the entire atmosphere instead of individual atmospheric layers. This procedure avoids as part of the solution scheme the inversion of a rather complex matrix thus resulting in high numerical efficiency. The model includes the absorption by atmospheric gases such as water vapor, CO2, O3 and NO2. This list can be extended if desired. Moreover absorption by aerosols and cloud particles is accounted for in addition to multiple scattering. A comparison with the rather accurate and already efficient transfer code of Zdunkowski et al. [6] shows that the present method is similarly accurate but numerically even more efficient. Therefore, this radiation scheme becomes very suitable for use in some circulation models of the atmosphere, such as prediction models of radiation fog.[/p]