Interactions between coherent eddies in the lower convective boundary layer
Interactions between coherent eddies in the lower convective boundary layer
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下对流边界层相干涡流之间的相互作用
DOI：
10.1007/bf00705662
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
J. Hacker
中科院分区：
文献类型：
--
作者：
Anthony G Williams;J. Hacker
利用仪器飞机飞行数据，研究了白天陆地对流条件下大气表面与混合层相互作用的过程。根据作者最近发表的一项研究的结果，讨论了分割运行平均统计的概况和时间序列图的例子，其中使用合成技术重建了连贯漩涡内的平均结构和流动。这一证据被用来支持表层羽流和混合层热柱之间相互作用机制的概念模型。大尺度混合层环流模式的下沉气流在地表附近形成发散气流，迫使地表形成辐合线（所谓的“热壁”），将空气引入混合层热气流的底部。羽流随着地面和自由对流层的高度逐渐聚集和合并，并沿着这些汇聚线向交叉点或“枢纽”处的大型“集热器”羽流移动。在“中心”上方是热气流，而来自羽流及其环境的空气包裹在上升过程中被强烈混合，导致条件采样方法区分它们的难度增加。观测到的深层混合层对流过程的影响，以及平均剖面的形式，支持了Kader和Yaglom（1990）最近提出的表层结构理论的改进。
The processes of interaction between the atmospheric surface and mixed layers in daytime convective conditions over land are studied using a data set obtained during flights by an instrumented aircraft. Profiles of partitioned run-averaged statistics and examples of time series plots are discussed in the light of results from a recently published study by the authors, in which the average structure and flow within coherent eddies was reconstruced using a compositing technique. This evidence is used to support a conceptual model of the mechanisms of interaction between surface-layer plumes and mixed-layer thermal columns. The divergent flow created near the surface by the downdraft arms of the large-scale mixed-layer circulation patterns, forces the development of lines of convergence in the surface layer (the so-called “thermal walls”), which channel air into the bases of the mixed-layer thermals. Plumes progressively group and merge together with height in the surface and free convection layers, and move along these convergence lines toward large “collector” plumes at the intersection points, or “hubs”. Above the “hubs” are the thermals, and air parcels originating from plumes and their environment are strongly mixed as they rise, leading to an increased difficulty of the conditional sampling method to distinguish between them. The observed influence of mixed-layer convective processes far down into the surface layer, and the form of the averaged profiles, supports recent refinements of the theory of surface-layer structure suggested in Kader and Yaglom (1990).