On the Size of Dominant Momentum Transporting Eddies in Stable Atmospheric Boundary Layers

The size of dominant momentum transporting eddies $L_{mt}$ in stable atmospheric boundary layers is poorly understood. This study demonstrates that the distance to the ground z is relevant in constraining $L_{mt}$ in weakly stable conditions (, where $\zeta$ is the stability parameter) and less relevant in moderately stable conditions (). The widely used Ozmidov scale, however, fails to represent $L_{mt}$ in moderately stable conditions. The low-wavenumber ends of the −5/3 scaling law regions in the spanwise and vertical velocity spectra correlate better with a shear-related length scale. Based on the characteristics of velocity spectra and the balance between kinetic energy and potential energy, a new length scale is proposed to indicate $L_{mt}$ for moderately stable conditions. Observational data show that this new length scale effectively characterizes $L_{mt}$ in moderately stable conditions. These findings can help develop better turbulence parameterization schemes for stable atmospheric boundary layers.