INERTIA-GRAVITY WAVE BREAKING IN 3 DIMENSIONS - PART I - CONVECTIVELYSTABLE WAVES

The three-dimensional breakdown of a large-amplitude, convectively sta ble inertia-gravity wave is examined numerically as a function of prim ary-wave frequency and amplitude. The results confirm that inertia-gra vity waves in this region of parameter space break down preferentially via shear instability. In low-frequency waves the instability is ubiq uitous, occurring simultaneously throughout the wave held, and the spe ctrum of instability energy is approximately, but not exactly, isotrop ic in azimuthal orientation. In higher-frequency waves, shear instabil ity develops adjacent to the region of reduced static stability, and d isplays a preference for intermediate azimuths (e.g., near 45 degrees) . Near-inertial waves experience the fastest growing instabilities. Th e growth rate of shear instability drops off rapidly as the wave frequ ency is increased and, for all frequencies, increases with increasing wave amplitude. At most frequencies, the onset of modal shear instabil ity occurs at a wave amplitude slightly above the theoretical stabilit y boundary determined from a local Richardson number argument.