Two-point properties of atmospheric turbulence very close to the ground: Comparison of a high resolution LES with theoretical models

Using the tools of large-eddy simulation (LES), rapid distortion theory and Eulerian kinematic simulation, two-point properties of turbulence are studied. It is shown how the boundary conditions in the present LES model are fully consistent with the new top-down understanding of atmospheric turbulence close to the ground, where the turbulence is analysed in terms of turbulent eddies impinging onto the ground, being distorted by the shear and the blocking by the wall, and experiencing the creation of an internal boundary layer within an eddy surface layer (ESL) with a height of a dozen metres. The question of very large streamwise structures is addressed, and it is shown that the k(-1) range measured in spectra for the streamwise velocity in the ESL in several recent field experiments can be found in LES, and corresponds to streaky structures. However, these streaky structures are different from the low Reynolds number streaks, which induce a k(-2) range in the spectrum. Finally, two-point vertical correlations are studied. In particular, effects of shear and of the slope of the spectrum are analysed.