The Onset of Resolved Boundary-Layer Turbulence at Grey-Zone Resolutions
The Onset of Resolved Boundary-Layer Turbulence at Grey-Zone Resolutions
复制标题
在灰色区域分辨率下解决边界层湍流的开始
DOI：
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发表时间：
2019
影响因子：
4.3
通讯作者：
R. Beare
中科院分区：
文献类型：
--
作者：
John C. Kealy;G. Efstathiou;R. Beare
数值天气预报（NWP）模式现在能够在100米至1公里的水平分辨率范围内运行，网格间距在尺度上类似于大气对流边界层（CBL）中存在的湍流漩涡。这种状态被称为湍流的“灰色地带”，其特点是来自已分解和子网格组件的显著贡献，代表了系统的主要运动。本研究探讨了在灰色地带模拟CBL的演变过程中，已解决的湍流（通常称为“自旋上升”的概念）的开始如何被延迟。我们确定了施加的势温伪随机扰动（$$\theta $$ θ）对求解场发展的重要性，表明没有这种扰动，求解湍流根本就不建立。当扰动被组织起来时，自旋上升可以更快地发展，并且我们发现通过应用一个理想的方差曲线来推导$$\theta $$ θ微扰值可以获得最早的自旋上升时间。当在混合层时间尺度$$t_{*}$$ t *之后的间隔施加摄动结构，而不是只在初始时间施加摄动时，显示出最有效的效果。我们还提出了一个对三维Smagorinsky湍流闭合的修正，其中Smagorinsky常数被一个尺度相关系数代替。(1)应用结构化$$\theta $$ θ微扰和(2)使用动态演化的Smagorinsky系数这两种方法都可以独立地促进更快的自旋上升，但当这两种方法同时应用时，效果最好。
Numerical weather prediction (NWP) models are now capable of operating at horizontal resolutions in the 100-m to 1-km range, a grid spacing similar in scale to that of the turbulent eddies present in the atmospheric convective boundary layer (CBL). Known as the ‘grey zone’ of turbulence, this regime is characterized by significant contributions from both the resolved and subgrid components to represent the dominant motions of the system. This study examines how the initiation of resolved turbulence – a concept commonly referred to as ‘spin-up’– can be delayed during the evolution of a simulated CBL in the grey zone. We identify the importance of imposed pseudo-random perturbations of potential temperature ($$\theta $$θ) for the development of the resolved fields showing that without such perturbations, resolved turbulence does not become established at all. When the perturbations are organized, spin-up can develop more rapidly, and we find that the earliest spin-up times can be achieved by applying an idealized profile of variance to derive the $$\theta $$θ perturbation values. The perturbation structures are shown to be most effective when applied at intervals following the mixed-layer time scale, $$t_{*}$$t∗, rather than perturbing only at the initial time. We also propose a modification to the three-dimensional Smagorinsky turbulence closure, in which the Smagorinsky constant is replaced by a scale-dependent coefficient. Both the approaches of: (1) applying structured $$\theta $$θ perturbations, and (2) using a dynamically-evolving Smagorinsky coefficient are shown to encourage faster spin-up independently of each other, but the best results clearly emerge when the two methods are applied concurrently.
基于指令的混合气象办公室 NERC 云模型
DOI：
10.1145/2832105.2832115
发表时间：
2015
期刊：
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影响因子：
--
作者：
Brown N
通讯作者：
Brown N
影响因子：
3
作者：
G. Efstathiou;R. Plant;Mary‐Jane M. Bopape
通讯作者：
G. Efstathiou;R. Plant;Mary‐Jane M. Bopape