Object‐Oriented Identification of Coherent Structures in Large Eddy Simulations: Importance of Downdrafts in Stratocumulus
Object‐Oriented Identification of Coherent Structures in Large Eddy Simulations: Importance of Downdrafts in Stratocumulus
复制标题
大涡模拟中相干结构的面向对象识别：层积云中下降气流的重要性
DOI：
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发表时间：
2019
影响因子：
5.2
通讯作者：
Rachel Honnert
中科院分区：
文献类型：
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作者：
F. Brient;F. Couvreux;N. Villefranque;C. Rio;Rachel Honnert
提出了一种新的方法来表征相干结构的大涡模拟。基于分别在地面和云顶发射的两种被动示踪剂，面向对象的框架允许单独表征流内的相干三维羽流。应用这种方法模拟海洋层积云顶部边界层的日循环表明，相干的上升气流和下降气流结构有助于大部分的热量和水分的总输送，虽然覆盖了一小部分的域体积。平均而言，下降气流对水汽通量的贡献与上升气流相等，而对热通量的贡献则大于上升气流。上升气流和下降气流对热量输送的相对贡献表现出较大的日变化周期，这表明云-湍流-辐射相互作用。我们的研究结果表明，层积云顶部边界层内的次网格下沉气流特性应该通过气候模式中的非局部质量通量参数化来表示。
A novel methodology is proposed to characterize coherent structures in large eddy simulations. Based on two passive tracers emitted respectively at the surface and at cloud top, the object‐oriented framework allows individual characterization of coherent tridimensional plumes within the flow. Applying this method in a simulation of the diurnal cycle of a marine stratocumulus‐topped boundary layer shows that coherent updraft and downdraft structures contribute to most of the total transport of heat and moisture, although covering a small part of the domain volume. On average, downdrafts contribute equally compared to updrafts for moisture fluxes and more than updrafts for heat fluxes. The relative contribution of updraft and downdraft objects to heat transport exhibits a large diurnal cycle, which suggests cloud‐turbulence‐radiation interaction. Our results suggest that subgrid downdraft properties within stratocumulus‐topped boundary layers should be represented through nonlocal mass‐flux parameterization in climate models.