Scaling of Turbulence and Microphysics in a Convection–Cloud Chamber of Varying Height
Scaling of Turbulence and Microphysics in a Convection–Cloud Chamber of Varying Height
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不同高度的对流云室中的湍流和微物理尺度
DOI：
10.1029/2022ms003304
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发表时间：
2023
影响因子：
6.8
通讯作者：
Shaw, Raymond A.
中科院分区：
文献类型：
--
作者：
Thomas, Subin;Yang, Fan;Ovchinnikov, Mikhail;Cantrell, Will;Shaw, Raymond A.
对流云室能够在稳态条件下测量湍流环境中的气溶胶和云微物理及其相互作用。增加对流云室的大小，同时保持施加的温差不变，会导致瑞利数、雷诺数和努塞尔数的增加。大涡模拟与面元微物理模式相结合，可以探索速度、时间和空间尺度的增加对云微物理特性的影响。模拟了具有固定高宽比和增加高度的对流云室，h=1，2，4，和(仅在干燥条件下)8米。主要发现是：速度涨落尺度为H1/3，与对流速度的Deardorff表达式一致，并暗示湍流关联时间尺度为H2/3，温度和其他标量波动尺度为−3/7。不同大小的燃烧室的液滴尺寸分布可以通过调整总气溶胶喷射率作为水平横截面面积来匹配(即，对于恒定展宽比，为asH_2)。气溶胶在某一点的喷射与在整个体积中的分布相比，对污染条件没有影响，但在清洁条件下会导致云滴尺寸分布变宽。与单独凝结增长相比，碰撞合并的云滴增长导致分布的右尾变宽，且随着云室高度的增加，右尾的大小和范围单调增加。这些结果对大气中的湍流、多云混合层(如雾层)的尺度也有影响。
The convection–cloud chamber enables measurement of aerosol and cloud microphysics, as well as their interactions, within a turbulent environment under steady‐state conditions. Increasing the size of a convection–cloud chamber, while holding the imposed temperature difference constant, leads to increased Rayleigh, Reynolds and Nusselt numbers. Large–eddy simulation coupled with a bin microphysics model allows the influence of increased velocity, time, and spatial scales on cloud microphysical properties to be explored. Simulations of a convection–cloud chamber, with fixed aspect ratio and increasing heights ofH= 1, 2, 4, and (for dry conditions only) 8 m are performed. The key findings are: Velocity fluctuations scale asH1/3, consistent with the Deardorff expression for convective velocity, and implying that the turbulence correlation time scales asH2/3. Temperature and other scalar fluctuations scale asH−3/7. Droplet size distributions from chambers of different sizes can be matched by adjusting the total aerosol injection rate as the horizontal cross‐sectional area (i.e., asH2for constant aspect ratio). Injection of aerosols at a point versus distributed throughout the volume makes no difference for polluted conditions, but can lead to cloud droplet size distribution broadening in clean conditions. Cloud droplet growth by collision and coalescence leads to a broader right tail of the distribution compared to condensation growth alone, and this tail increases in magnitude and extent monotonically as the increase of chamber height. These results also have implications for scaling within turbulent, cloudy mixed‐layers in the atmosphere, such as fog layers.
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