Universal behavior of Fourier spectra of turbulence in the atmospheric boundary layer when the spectral energy and the frequency (or wavenumber) are made dimensionless using the appropriate boundary layer scales. Separate spectral similarity relationships have been found for the surface layer and for the convective mixed layer. See similarity theory, dimensional analysis, fast Fourier transform, Buckingham Pi theory, inertial subrange, Kolmogorov's similarity hypotheses.