Radiating and nonradiating modes of secondary instability in a gravity-wave critical layer

Abstract

The structure and growth rates of preferred modes of secondary instability - within or near regions of potential temperature overturning in the wave field - are discussed. Model instabilities, which appear to be primarily convective, are of two kinds. The expected mode of convective instability is nonradiating, trapped within the region of overturning. A new "radiating' mode of instability was also obtained that has a preferred zonal scale, grows to observable amplitude prior to the nonradiating mode, and extends into the adjacent stable regions of the wave field. As a result, this mode is important in the transition to turbulence and may affect momentum deposition and turbulent mixing due to gravity-wave breaking. -from Authors