Salesky S T, Anderson W
School of Meteorology, The University of Oklahoma, Norman, Oklahoma 73072, USA.
Mechanical Engineering Department, The University of Texas at Dallas, Richardson, Texas 75080, USA.
Phys Rev Lett. 2020 Sep 18;125(12):124501. doi: 10.1103/PhysRevLett.125.124501.
Since its inception in the 1940s, Monin-Obukhov similarity theory (MOST), which relates turbulent fluxes to mean vertical gradients in the lower atmosphere, has become ubiquitous for predicting surface fluxes of quantities transported by the flow in numerical weather, climate, and hydrological forecasting models. Despite its widespread use, MOST does not account for the effects of large coherent structures in the flow, which modulate the amplitude of turbulent fluctuations, and are responsible for a large fraction of the total transport. Herein, we demonstrate that the incorporation of the large-scale streamwise velocity u_{l}(x,t)=G_{δ}⋆u(x,t), where G_{δ} is a low-pass filtering kernel, into dimensional analysis leads to an additional dimensionless parameter α(x,t), which captures the modulating influence of these structures on flux-gradient relationships. Atmospheric observations and large-eddy simulations are used to demonstrate that observed deviations from MOST can indeed be explained by this new parameter; coherent structures induce an alternating loading and unloading of the mean velocity gradient near the surface.
自20世纪40年代提出以来，莫宁 - 奥布霍夫相似性理论（MOST）将湍流通量与低层大气中的平均垂直梯度联系起来，在数值天气、气候和水文预报模型中预测由气流输送的量的表面通量时已无处不在。尽管其应用广泛，但MOST并未考虑气流中大型相干结构的影响，这些结构调节湍流波动的幅度，并负责大部分的总输送。在此，我们证明将大尺度流向速度(u_{l}(x,t)=G_{δ}⋆u(x,t))（其中(G_{δ})是低通滤波核）纳入量纲分析会导致一个额外的无量纲参数(α(x,t))，它捕捉了这些结构对通量 - 梯度关系的调制影响。利用大气观测和大涡模拟来证明，观测到的与MOST的偏差确实可以用这个新参数来解释；相干结构在地表附近引起平均速度梯度的交替加载和卸载。
