Extended Abstract (120K)JP4.19
Possible implications of droplet clustering for radiative transfer in clouds (Formerly Paper Number P5.4)
Alexander B. Kostinski, Michigan Technological University, Houghton, MI; and R. A. Shaw
Existence of correlations in the spatial positions of cloud droplets appears likely on various scales (e.g., Kostinski and Shaw, J. Fluid Mech., 2001). Do such correlations affect radiative transfer in clouds? Using the language of Poisson processes, it has been recently shown (Kostinski, J. Opt. Soc. Am. A, 2001) that such correlations may lead to deviations from the traditional exponential extinction (slower decay with distance). This conclusion is in agreement with previous work by others, but achieved by entirely different arguments. Exponential decay, described by the Beer-Lambert law, arises in a special case when the medium contains no correlations. Also, it has been recently shown (Shaw, Kostinski, and Lanterman, J. Quant. Spect. Rad. Tran., 2002) that negative correlations can lead to faster-than-exponential extinction. Monte Carlo simulations are described which confirm both sub-exponential and super-exponential regimes when the volume-averaged pair correlation function is positive/negative and that the Beer-Lambert law is recovered when correlations vanish. The simulations and preliminary theoretical analysis also suggest that a modified exponential extinction regime is established in the limit of a long propagation path (much longer than the coherence length). This regime involves an "effective" optical depth which depends of the pair correlation function of the medium. We discuss possible implications of these results to the problem of radiative transfer in cloudy atmospheres, where the pair correlation function previously has been shown to be strongly scale-dependent.
Joint Poster Session 4, Cloud Variability (Joint between 11th Cloud Physics and 11th Atmospheric Radiation)
Thursday, 6 June 2002, 1:00 PM-3:00 PM
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