Wave-mean-flow interactions in a gravity wave packet critical layer

This talk presents numerical simulations of the nonlinear interaction of an internal gravity wave packet with the mean wind in the vicinity of a critical layer. The theories associated with gravity wave critical layers may explain many aspects of the dynamics of orographic waves, e.g., momentum transport, wave breaking and the generation of turbulence. Most previous studies of critical layer phenomena have dealt with spatially periodic waves; however, that is not a very realistic representation of a disturbance forced by isolated topography. In the investigations described here, the disturbance takes the form of a horizontally localized wave packet, rather than a monochromatic wave. The results of the numerical simulations are contrasted with those obtained in the monochromatic case. It is found that the spatial localization delays the onset of the nonlinear breakdown in the critical layer so that the disturbance remains convectively stable well into the nonlinear regime.