Wavenumber spectra of horizontal wind and temperature measured with WINDII, Part II: diffusive effect on spectral formation

Vertical and horizontal wavenumber spectra of horizontal wind and temperatu re observed with WINDII are used to examine the effect of diffusion process on the spectral evolution. At small wavenumbers, the spectral slope is gen erally found to be close to zero, due to restriction of diffusion process. In order to better describe the situation, the frequency-dependent diffusiv ity used in the diffusive model (Gardner, 1994, journal of Geophysical Rese arch 99, 20,601-20,622) is generalized to include a wavenumber dependence. The saturated-cascade model (Dewan, 1991; 1994, Geophysical Research Letter s 21, 817-820) are transformed into a diffusive form by assuming the wave e nergy to be dissipated through diffusion. The observed spectra are compared with the diffusive and cascade models, as well as the non-diffusive model (Gardner et al., 1993a, Journal of Geophysical Research 98, 1035-1049). Our results show that diffusion process plays an important role in maintaining the shapes and amplitudes of vertical wavenumber spectra, but less signifi cant for horizontal wavenumber spectra at the observed large wavelengths. ( C) 2000 Elsevier Science Ltd. All rights reserved.