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DOI10.5194/acp-20-7895-2020
Technical note: Equilibrium droplet size distributions in a turbulent cloud chamber with uniform supersaturation
Krueger S.K.
发表日期2020
ISSN16807316
起始页码7895
结束页码7909
卷号20期号:13
英文摘要In a laboratory cloud chamber that is undergoing Rayleigh-Bénard convection, supersaturation is produced by isobaric mixing. When aerosols (cloud condensation nuclei) are injected into the chamber at a constant rate, and the rate of droplet activation is balanced by the rate of droplet loss, an equilibrium droplet size distribution (DSD) can be achieved. We derived analytic equilibrium DSDs and probability density functions (PDFs) of droplet radius and squared radius for conditions that could occur in such a turbulent cloud chamber when there is uniform supersaturation. We neglected the effects of droplet curvature and solute on the droplet growth rate. The loss rate due to fallout that we used assumes that (1) the droplets are well-mixed by turbulence, (2) when a droplet becomes sufficiently close to the lower boundary, the droplet's terminal velocity determines its probability of fallout per unit time, and (3) a droplet's terminal velocity follows Stokes' law (so it is proportional to its radius squared). Given the chamber height, the analytic PDF is determined by the mean supersaturation alone. From the expression for the PDF of the radius, we obtained analytic expressions for the first five moments of the radius, including moments for truncated DSDs. We used statistics from a set of measured DSDs to check for consistency with the analytic PDF. We found consistency between the theoretical and measured moments, but only when the truncation radius of the measured DSDs was taken into account. This consistency allows us to infer the mean supersaturations that would produce the measured PDFs in the absence of supersaturation fluctuations. We found that accounting for the truncation radius of the measured DSDs is particularly important when comparing the theoretical and measured relative dispersions of the droplet radius. We also included some additional quantities derived from the analytic DSD: droplet sedimentation flux, precipitation flux, and condensation rate. © 2020 Author(s).
关键词aerosolcloud condensation nucleuscloud microphysicscondensationconvective systemdropletequilibriumprobability density functionquantitative analysissize distributionsupersaturationturbulence
语种英语
来源机构Atmospheric Chemistry and Physics
文献类型期刊论文
条目标识符http://gcip.llas.ac.cn/handle/2XKMVOVA/131941
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Krueger S.K.. Technical note: Equilibrium droplet size distributions in a turbulent cloud chamber with uniform supersaturation[J]. Atmospheric Chemistry and Physics,2020,20(13).
APA Krueger S.K..(2020).Technical note: Equilibrium droplet size distributions in a turbulent cloud chamber with uniform supersaturation.,20(13).
MLA Krueger S.K.."Technical note: Equilibrium droplet size distributions in a turbulent cloud chamber with uniform supersaturation".20.13(2020).
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