INERTIA-GRAVITY WAVE BREAKING IN 3 DIMENSIONS - PART II - CONVECTIVELY UNSTABLE WAVES

The three-dimensional breakdown of a large-amplitude, convectively uns table inertia-gravity wave is examined numerically as a function of pr imary-wave frequency and amplitude. The results confirm that near-iner tial waves break down preferentially via shear instability even when t he primary wave is initially overturned. As in the convectively stable near-inertial regime, the spectrum of instability energy is approxima tely isotropic in azimuthal orientation. At intermediate frequencies, wave breakdown is triggered by a transverse shear instability in the r egion of overturning. This behavior, displaying a clear preference for instability with horizontal component of wavevector in the transverse direction, is different from the breakdown of convectively stable wav es at intermediate frequency examined in Part I. As the primary-wave f requency is increased further, shear instabilities once again develop in the transverse direction, but they are modified by convective insta bility as the billows reach finite amplitude. The influence of transve rse vertical shear becomes progressively weaker as the wave frequency approaches the buoyancy frequency. In this limit, transverse convectio n leads to wave-collapse, and there is no preferred scale of instabili ty.