具有下沉运动的稳定边界层：真正稳态的尺度与相似性
Stable Boundary Layers with Subsidence: Scaling and Similarity of the Truly Steady State
AI总结：
本文通过大涡模拟研究了受大尺度下沉运动影响的稳定边界层的真正稳态，确定了三个控制无量纲群，提出了经验关联和新地转曳力律以估计流动特性，并验证了其与Monin-Obukhov相似理论的一致性。
摘要：
本文通过采用固定地表温度和线性下沉速度剖面的大涡模拟（LESs），研究了受大尺度下沉运动影响的稳定边界层（SBL）。这些边界层达到了真正的稳态，在该状态下，热平衡由地表冷却与下沉引起的加热之间的平衡来建立。我们通过用地转风和科里奥利频率对控制方程进行尺度分析，确定了三个控制无量纲群，并系统地研究了这些外部参数对稳态下全局流动特性和平均剖面的影响。当下沉率或浮力数增加时，SBL深度、低空急流和湍流动量通量的幅值会减小，而地表热通量则增强。温度和热通量的无量纲平均剖面形状主要由下沉率决定，而它们对于变化的浮力和地表罗斯贝数则表现出重叠。我们针对稳定性参数 $h_θ/L_O$ 和一个热形状因子建立了经验关联，并提出了一种新的单向地转曳力律，以构成一组闭合方程，从而根据外部参数估计相关的流动特性。与 LES 数据相比，摩擦速度和地表热通量的估计误差小于 5%，SBL 深度 $h_θ$ 的估计误差最多为 10%。在表面层内，具有下沉运动的稳态 SBL 的无量纲速度和温度梯度与 Monin-Obukhov 相似理论表现出可接受的一致性，而当使用包含 $h_θ/L_O$ 的最近提出的混合尺度参数时，剖面的重叠性得到了改善。
英文摘要：
The stable boundary layer (SBL) subjected to large-scale subsidence is studied through large-eddy simulations (LESs) with fixed surface temperature and a linear subsidence velocity profile. These boundary layers reach a truly steady state, where thermal equilibrium is established by a balance between surface cooling and subsidence-induced heating. We identify three governing dimensionless groups by scaling the governing equations with the geostrophic wind and Coriolis frequency, and systematically investigate the impact of these external parameters on global flow properties and mean profiles in the steady state. The SBL depth, low-level jet, and the magnitude of the turbulent momentum flux are reduced when the subsidence rate or Buoyancy number increases, while surface heat flux is enhanced. The shape of normalized mean profiles of temperature and heat flux is mainly determined by the subsidence rate, while they collapse for varying buoyancy and surface Rossby numbers. We develop empirical correlations for the stability parameter $h_θ/L_O$ and a thermal shape factor, and propose a new unidirectional geostrophic drag law, to form a closed set of equations that estimates relevant flow properties from external parameters. The estimation errors compared to the LES data are less than 5% for friction velocity and surface heat flux, and at most 10% for the SBL depth $h_θ$. Within the surface layer, dimensionless velocity and temperature gradients in the steady SBL with subsidence show acceptable agreement to Monin-Obukhov similarity theory, while the collapse is improved when a recently proposed mixed scaling parameter, that includes $h_θ/L_O$, is used.
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