Third‐order resonant interaction of atmospheric gravity waves

Abstract

Relative to the extensive studies of third‐order nonlinearity for oceanic gravity waves, third‐order interaction of atmospheric gravity waves has drawn little attention. By numerical experiments with a two‐dimensional, fully nonlinear model, third‐order resonant excitation of atmospheric gravity waves is clearly exhibited. The numerical results indicate that third‐order interaction can take place in the atmosphere, and significant energy exchange occurs in interaction. Wave energy mainly transfers from the high frequency primary wave to the excited wave, and an intense secondary wave can strengthen this energy transfer, which is consistent with the results in second‐order interaction. In the whole process of interaction, both the wave numbers and frequencies of the interacting waves are in good agreement with the third‐order resonant conditions. Third‐order resonance arises through direct interaction of waves that satisfy the corresponding resonant conditions, and there is not a second‐order harmonic or an intermediate forced mode involved in nonlinear interaction. Because gravity waves in the middle and upper atmosphere generally have rather large amplitudes, strong third‐order interaction may frequently occur. Thus, this nonlinearity may be regarded as a significant local source for high frequency gravity waves in the middle and upper atmosphere.