Effect of Cloudiness on the Transfer of Solar Energy Through Realistic Model Atmospheres

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  • a IBM Scientific Center, Palo Alto, Calif. 94304
  • b IBM T. J. Walson Research Center, Yorkiown Heights, N.Y. 10598
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Abstract

Extensive calculations of the effect of cloudiness on the solar energy absorbed, reflected and transmitted by nonhomogeneous plane-parallel atmospheric models have been carried out with the object of treating the radiation transfer in as comprehensive a manner as possible. The concentration of aerosol (spherical particles with size distribution and refractive index independent of height), ozone and water vapor were specified for 50 basic layers of equal geometric thickness from the surface to 50 km. A stratus cloud layer with a liquid water content of 0.0128 g m–3 was introduced between the 3 and 4 km levels of the models. The solar spectrum (0.285–2.5μm) was divided into 83 intervals with appropriate functions representing the scattering and absorption of gases, and the aerosol and liquid water drops assigned to each, the refractive indices of the aerosol and water drops taken to be wavelength-independent.

For accurate computations of the upward and downward fluxes for a given model at a given wavelength, basic layers with total optical thicknesses greater than 0.02 were subdivided so that total optical thickness of no layer exceeded 0.02. Fluxes at all levels of such a model were calculated by using the direct solution of the spherical harmonics approximation to the basic transfer equation discussed by Dave and Canosa.

Results will be presented for eight model atmospheres containing gases, aerosol of different concentration and refractive index, and, in two models, a stratus cloud of water drops, showing the absorbed, diffusely reflected, and diffusely as well as directly transmitted (spectrally integrated) solar energy for a range of solar zenith angles and Lambert ground reflectivities.

Abstract

Extensive calculations of the effect of cloudiness on the solar energy absorbed, reflected and transmitted by nonhomogeneous plane-parallel atmospheric models have been carried out with the object of treating the radiation transfer in as comprehensive a manner as possible. The concentration of aerosol (spherical particles with size distribution and refractive index independent of height), ozone and water vapor were specified for 50 basic layers of equal geometric thickness from the surface to 50 km. A stratus cloud layer with a liquid water content of 0.0128 g m–3 was introduced between the 3 and 4 km levels of the models. The solar spectrum (0.285–2.5μm) was divided into 83 intervals with appropriate functions representing the scattering and absorption of gases, and the aerosol and liquid water drops assigned to each, the refractive indices of the aerosol and water drops taken to be wavelength-independent.

For accurate computations of the upward and downward fluxes for a given model at a given wavelength, basic layers with total optical thicknesses greater than 0.02 were subdivided so that total optical thickness of no layer exceeded 0.02. Fluxes at all levels of such a model were calculated by using the direct solution of the spherical harmonics approximation to the basic transfer equation discussed by Dave and Canosa.

Results will be presented for eight model atmospheres containing gases, aerosol of different concentration and refractive index, and, in two models, a stratus cloud of water drops, showing the absorbed, diffusely reflected, and diffusely as well as directly transmitted (spectrally integrated) solar energy for a range of solar zenith angles and Lambert ground reflectivities.

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