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

Abstract

Vertical and horizontal wavenumber spectra of horizontal wind and temperature observed with WINDII are used to examine the effect of diffusion process on the spectral evolution. At small wavenumbers, the spectral slope is generally found to be close to zero, due to restriction of diffusion process. In order to better describe the situation, the frequency-dependent diffusivity used in the diffusive model (Gardner, 1994, Journal of Geophysical Research 99, 20,601–20,622) is generalized to include a wavenumber dependence. The saturated-cascade model (Dewan, 1991; 1994, Geophysical Research Letters 21, 817–820) are transformed into a diffusive form by assuming the wave energy 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 significant for horizontal wavenumber spectra at the observed large wavelengths.