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Article

Light Scattering in a Turbulent Cloud: Simulations to Explore Cloud-Chamber Experiments

1
Department of Physics and Atmospheric Sciences Program, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, USA
2
Department of Physics and Astronomy, College of Charleston, 66 George St., Charleston, SC 29424, USA
*
Author to whom correspondence should be addressed.
Atmosphere 2020, 11(8), 837; https://doi.org/10.3390/atmos11080837
Received: 24 June 2020 / Revised: 31 July 2020 / Accepted: 3 August 2020 / Published: 7 August 2020
(This article belongs to the Special Issue The Motion of Particles in Turbulence)
Radiative transfer through clouds can be impacted by variations in particle number size distribution, but also in particle spatial distribution. Due to turbulent mixing and inertial effects, spatial correlations often exist, even on scales reaching the cloud droplet separation distance. The resulting clusters and voids within the droplet field can lead to deviations from exponential extinction. Prior work has numerically investigated these departures from exponential attenuation in absorptive and scattering media; this work takes a step towards determining the feasibility of detecting departures from exponential behavior due to spatial correlation in turbulent clouds generated in a laboratory setting. Large Eddy Simulation (LES) is used to mimic turbulent mixing clouds generated in a laboratory convection cloud chamber. Light propagation through the resulting polydisperse and spatially correlated particle fields is explored via Monte Carlo ray tracing simulations. The key finding is that both mean radiative flux and standard deviation about the mean differ when correlations exist, suggesting that an experiment using a laboratory convection cloud chamber could be designed to investigate non-exponential behavior. Total forward flux is largely unchanged (due to scattering being highly forward-dominant for the size parameters considered), allowing it to be used for conditional sampling based on optical thickness. Direct and diffuse forward flux means are modified by approximately one standard deviation. Standard deviations of diffuse forward and backward fluxes are strongly enhanced, suggesting that fluctuations in the scattered light are a more sensitive metric to consider. The results also suggest the possibility that measurements of radiative transfer could be used to infer the strength and scales of correlations in a turbulent cloud, indicating entrainment and mixing effects. View Full-Text
Keywords: particle clustering; light scattering; Monte Carlo ray tracing; large eddy simulation; turbulent clouds; inhomogeneous clouds; radiative transfer in spatially correlated media particle clustering; light scattering; Monte Carlo ray tracing; large eddy simulation; turbulent clouds; inhomogeneous clouds; radiative transfer in spatially correlated media
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MDPI and ACS Style

Packard, C.D.; Larsen, M.L.; Thomas, S.; Cantrell, W.H.; Shaw, R.A. Light Scattering in a Turbulent Cloud: Simulations to Explore Cloud-Chamber Experiments. Atmosphere 2020, 11, 837. https://doi.org/10.3390/atmos11080837

AMA Style

Packard CD, Larsen ML, Thomas S, Cantrell WH, Shaw RA. Light Scattering in a Turbulent Cloud: Simulations to Explore Cloud-Chamber Experiments. Atmosphere. 2020; 11(8):837. https://doi.org/10.3390/atmos11080837

Chicago/Turabian Style

Packard, Corey D., Michael L. Larsen, Subin Thomas, Will H. Cantrell, and Raymond A. Shaw. 2020. "Light Scattering in a Turbulent Cloud: Simulations to Explore Cloud-Chamber Experiments" Atmosphere 11, no. 8: 837. https://doi.org/10.3390/atmos11080837

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