On Modelling Nucleation and Condensation Theory in Eulerian Spatial Domain

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  • 1 Atmospheric Environment Service, Downsview, Ontario, Canada
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Abstract

One-dimensional, kinematical microphysical cloud models are used to study two numerical aspects associated with modelling the initial microphysical stages of cloud growth in Eulerian spatial domain. First, the high-frequency oscillations in the spatially integrated nucleation rate and maximum supersaturation which became apparent in Clark’s model calculations are reproduced in the present paper and their cause and effect studied. Second, the spatial and radius resolution requirements for calculations of the initial phases of cloud development are studied. It is found that rather high spatial as well as radius resolution are required to obtain a reasonable degree of convergence for the solution of the droplet spectrum coefficient of dispersion for a case where an eddy mixing coefficient K=2 m2 sec−1 was used.

The effect of eddy mixing on droplet spectral broadening is investigated where adequate spatial and radius resolution are used. The results indicate that mixing has a rather strong effect on the coefficient of dispersion for the droplet spectrum. Arbitrary values of K=0, 1, 2 and 4 m2 sec−1 were Used where it was found that results similar to those of Warner were obtained for the K=0 case only.

The gamma distribution parameterization of Clark has been generalized to include condensation coefficient effects. The original parameterization scheme has been given a far more thorough comparison with a finite-difference model in one spatial dimension.

Abstract

One-dimensional, kinematical microphysical cloud models are used to study two numerical aspects associated with modelling the initial microphysical stages of cloud growth in Eulerian spatial domain. First, the high-frequency oscillations in the spatially integrated nucleation rate and maximum supersaturation which became apparent in Clark’s model calculations are reproduced in the present paper and their cause and effect studied. Second, the spatial and radius resolution requirements for calculations of the initial phases of cloud development are studied. It is found that rather high spatial as well as radius resolution are required to obtain a reasonable degree of convergence for the solution of the droplet spectrum coefficient of dispersion for a case where an eddy mixing coefficient K=2 m2 sec−1 was used.

The effect of eddy mixing on droplet spectral broadening is investigated where adequate spatial and radius resolution are used. The results indicate that mixing has a rather strong effect on the coefficient of dispersion for the droplet spectrum. Arbitrary values of K=0, 1, 2 and 4 m2 sec−1 were Used where it was found that results similar to those of Warner were obtained for the K=0 case only.

The gamma distribution parameterization of Clark has been generalized to include condensation coefficient effects. The original parameterization scheme has been given a far more thorough comparison with a finite-difference model in one spatial dimension.

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