Aerosol‐induced mechanisms for cumulus congestus growth
Aerosol‐induced mechanisms for cumulus congestus growth
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DOI：
10.1002/2015jd023743
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发表时间：
2015-09
期刊：
影响因子：
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通讯作者：
Amanda Sheffield;S. Saleeby;S. C. Heever
中科院分区：
文献类型：
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作者：
Amanda Sheffield;S. Saleeby;S. C. Heever
热带对流已被观测到包含三种云模式，中间是积云。密集云的作用是湿润热带大气，可能是混合相的，有时会超过冰点逆温，在那里它们可能发展成更深的对流。本研究探讨了在辐射对流平衡（RCE）状态下运行的理想解云模式模拟中，气溶胶浓度增强对密集云生长的影响。利用区域大气模拟系统（RAMS）完成了高分辨率、长时间的模拟。地面以上2至4公里之间的气溶胶浓度从清洁到污染的情况有所不同，以表示撒哈拉沙尘在大西洋上空的平流。在模拟达到RCE后，使用10天的模式输出对每个气溶胶模拟中的群集种群进行统计分析。结果表明，在污染更严重的条件下，拥堵会产生更多的云水和冰块，增强上升气流强度，并且拥堵云顶的数量增加，这些云顶延伸到冰点以上。在污染条件下，数量更多、体积更小的云滴种群的气相沉积增长增强，以及随后云的暖相区域潜热释放的增加，被发现是这些云系统对流增强的重要因素。与冷池和冷凝物负荷相关的气溶胶反馈也影响上升气流强度，并与暖相活化过程相反。
Tropical convection has been observed to contain three cloud modes, the middle of which is cumulus congestus clouds. Congestus clouds act to moisten the tropical atmosphere, may be mixed‐phase, and on occasion surpass the freezing level inversion from where they may develop into deeper convection. This study investigates the impacts of enhanced aerosol concentrations on the growth of congestus clouds produced in idealized cloud‐resolving model simulations run under a state of radiative convective equilibrium (RCE). High‐resolution, long‐duration simulations were completed using the Regional Atmospheric Modeling System (RAMS). Aerosol concentrations between 2 and 4 km above ground level were varied from clean to polluted conditions in order to represent the advection of Saharan dust over the Atlantic Ocean. The congestus populations within each aerosol simulation are statistically analyzed using 10 days of model output after the simulation reaches RCE. Results indicate that congestus in more polluted conditions produce greater amounts of cloud water and ice mass, enhanced updraft strengths, and an increase in the number of congestus cloud tops that extend above the freezing level. Enhanced vapor depositional growth on the populations of more numerous, smaller cloud droplets in the polluted conditions, and the subsequent increase in latent heat release in the warm phase regions of the cloud, is found to be important factors in convective invigoration of these cloud systems. Aerosol feedbacks associated with cold pools and condensate loading also influence the updraft strength and act in opposition to the warm phase invigoration processes.