SHEAR EXCITATION OF GRAVITY WAVES. PART II: UPSCALE SCATTERING FROM KELVIN-HELMHOLTZ WAVES.

Abstract

Upscale scattering of Kelvin-Helmholtz waves to gravity shear waves involves the nonlinear interaction of two Kelvin-Helmholtz waves with wavenumbers k and k prime to produce a wave with wavenumber k - k prime . Calculations show that the process produces long-wavelength radiating gravity waves in atmospheric conditions that favor Kelvin-Helmholtz instabilities. Both line and continuum evaluations are presented in the context of the unstable tropospheric jet. It is shown that even when the unstable shear in the jet is confined to a shallow sublayer, producing markedly small-scale Kelvin-Helmholz instabilities, upscale scattering to the large-scale waves is an efficient process. Refs.