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 andEulerian kinematic simulation, two-point properties of turbulenceare studied. It is shown how the boundary conditions in thepresent LES model are fully consistent with the new top-down understanding ofatmospheric turbulence close to the ground, wherethe turbulence is analysed in terms of turbulent eddies impinging ontothe ground, being distorted by the shear and the blocking by the wall,and experiencing the creation of an internal boundary layer within aneddy surface layer (ESL) with a height of a dozen metres.The question of very large streamwise structures is addressed, and itis shown that the k^-1 range measured in spectra for the streamwisevelocity in the ESL in several recent field experiments can be found in LES, and corresponds to streaky structures. However, thesestreaky structures are different from the low Reynolds number streaks,which induce a k^-2 range in the spectrum. Finally, two-point verticalcorrelations are studied. In particular, effects of shear and of the slope of thespectrum are analysed.