Entrainment of aerosols and their activation in a shallow cumulus cloud studied with a coupled LCM-LES approach
Entrainment of aerosols and their activation in a shallow cumulus cloud studied with a coupled LCM-LES approach
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DOI：
10.1016/j.atmosres.2014.12.008
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发表时间：
2015-04-01
影响因子：
5.5
通讯作者：
Noh, Y.
中科院分区：
文献类型：
--
作者：
Hoffmann, F.;Raasch, S.;Noh, Y.
本研究利用嵌入拉格朗日云模型（LCM）的大涡模拟（LES）研究了携流如何影响浅积云中气溶胶的活化，其中气溶胶和液滴被明确地视为拉格朗日粒子。分析了被云底中心上升气流和云底上方湍流混合（侧向夹带）夹带的气溶胶的活化过程。云基气溶胶和侧夹带气溶胶分别占云内所有活化气溶胶的70%和30%，侧夹带颗粒主导云基以上的活化（二次活化），其中云基气溶胶约占三分之一。正如在许多参数化中所假定的那样，云基气溶胶的激活受到最大饱和度的限制。然而，侧向夹带气溶胶的激活取决于湍流的程度，这限制了激活的可用时间，并将激活限制在中等大小的气溶胶，这需要最短的激活时间。随着环境气溶胶浓度的增加，侧向夹带气溶胶的活化变得更加重要。(C) 2014 Elsevier B.V.版权所有
This study investigates how entrainment affects the activation of aerosols in a shallow cumulus cloud using large-eddy simulations (LES) with an embedded Lagrangian cloud model (LCM) in which aerosols and droplets are explicitly treated as Lagrangian particles. The activation process is analyzed for aerosols entrained (i) by the central updraft at cloud base and (ii) by turbulent mixing above cloud base (lateral entrainment). Cloud base aerosols and laterally entrained aerosols contribute to all activated aerosols inside the cloud by fractions of 70% and 30%, respectively, laterally entrained particles dominate the activation above cloud base (secondary activation), to which cloud base aerosols contribute about one third. As assumed in many parameterizations, the activation of cloud base aerosols is limited by the maximum saturation. However, the activation of laterally entrained aerosols is determined by the degree of turbulence, limiting the time available for activation and restricting the activation to intermediate sized aerosols, which demand the shortest time for activation. As the environmental aerosol concentration increases, activation of laterally entrained aerosols becomes more important. (C) 2014 Elsevier B.V. All rights reserved.