Some impact of pollutants on the development and optical properties of stratocumulus clouds
Some impact of pollutants on the development and optical properties of stratocumulus clouds
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污染物对层积云的发展和光学特性的一些影响
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
R. Wood
中科院分区：
文献类型：
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作者：
S. Ghosh;P. Jonas;R. Wood
最近的两个主要的现场项目-欧洲云辐射实验（EUREX）和气溶胶表征实验II（ACE-2）-广泛分析了被大陆空气污染的层积云的动力学，微物理和辐射属性。虽然现在有一套广泛的动力学和微物理数据，但没有任何匹配的理论建模研究。为了充分理解和数值模拟为我们的案例研究选择的两个云的动力学，微物理，辐射和化学性质之间的相互作用，需要一个完整的三维大涡模拟（LES）模型耦合到一个全尺寸的解析微物理模型，其中计算成本将是禁止的。在这项研究中，我们已经“优化”的经典凯斯勒参数化方案，使其能够有效地区分干净和污染的云。我们使用优化方案执行LES运行以研究云的形态和动力学，然后使用相同环境条件下运行的第二个一维微物理包裹模型来研究污染对云的影响以及液滴光谱演变。这个过程产生了非常好的协议与观察在适度的计算费用。结果表明，以十亿分之一体积（p. p. b. v.）计的硝酸（HNO 3）蒸汽可在空气中蒸发。与无酸模拟相比，范围通过增加云滴的数量和降低平均尺寸来影响云的形成。HNO 3污染对EUREX案例研究的影响是显而易见的，因为这种云接近空气污染物的来源。使用10 p. p. b. v.的HNO 3，我们能够与液滴有效半径的观测结果以及光学深度变化的观测结果取得良好的一致性。对于远离污染物来源形成的ACE-2云，即使在典型的“污染”天，当环境HNO 3的体积为万亿分之0.5时，液滴浓度对HNO 3的变化也不敏感。
Two major recent field programmes—the European Cloud Radiation Experiment (EUCREX) and the Aerosol Characterization Experiment II (ACE‐2)‐have extensively analysed the dynamical, microphysical and radiative attributes of stratocumulus clouds contaminated by continental air. Although an extensive set of dynamical and microphysical data are now available, there are no accounts of any matching theoretical modelling studies. To fully understand and numerically model the interplay between the dynamics, microphysics, radiative and chemical properties of the two clouds chosen for our case‐studies would require a full three‐dimensional large‐eddy simulation (LES) model coupled to a full‐size resolving microphysical model where the computational costs would be prohibitive. In this study we have ‘optimized’ the classic Kessler parametrization scheme so that it is effectively able to distinguish between clean and contaminated clouds. We perform LES runs with the optimized scheme to study the morphology and the dynamics of the clouds and then use a second one‐dimensional microphysical parcel model run with identical environmental conditions to study the effects of pollution on the clouds as well as the droplet spectral evolution. This procedure yields extremely good agreement with observations at modest computational expense. It is shown that nitric acid (HNO3) vapour in the parts per billion by volume (p.p.b.v.) range affects cloud formation by increasing the number of cloud droplets and decreasing the mean size compared to an acid‐free simulation. The effects of HNO3 contamination on the EUCREX case‐study is evident owing to the proximity of this cloud to sources of air pollutants. With 10 p.p.b.v. of HNO3, we are able to achieve good agreement with the observations of the droplet effective radii as well as with observations of the optical‐depth variation. For the ACE‐2 cloud which formed further away from sources of pollutants, even on a typical ‘polluted’ day when the ambient HNO3 was ∼5 parts per trillion by volume, the drop concentration was found to be insensitive to changes in the HNO3.