Empirical data on turbulence in the surface layer of the atmosphere

Abstract

The statistical characteristics of turbulence in the atmospheric boundary layer are relatively stable when averaged over a time of the order of 10 to 20 minutes. The large-scale turbulence is related to a set of ‘external parameters': g/T¯, q/cpp, and v*, where T is the average temperature, q the vertical component of the turbulent heat flux, and v* the friction velocity. The smallerscale turbulence is related to a set of external parameters consisting of the rate of dissipation of turbulent energy, the rate of decay of inhomogeneities of the temperature field, and the buoyancy parameter g/T¯. For each of these ranges of the turbulence spectrum, two similarity expressions which are functions of these external parameters are determined. Three limiting cases of turbulence in the atmospheric boundary layer are considered: (a) neutral stratification where q must be eliminated from the similarity expressions; (b) strong instability where v* is eliminated; (c) strong stability where the height above the ground z must be eliminated from the similarity expressions. The time spectra of vertical velocity and of temperature are found and compared with experimental data. Spectra of turbulent stress and heat flux are also considered, and experimental data available about these spectra show that, at a height of 1 meter, the main contribution to the turbulent friction and heat flux is due to wavelengths of horizontal inhomogeneities of the order of some meters or even tens of meters.