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Density stratification is the essential underlying physical model for atmospheric and oceanic flow. As a first step to investigating the mechanisms of stratified turbulence, linearÌýstability plays a critical role in determining under what conditions aÌýflow remains stable or unstable. In the study of transition to stratified turbulence, a common vortex model, known as theÌýLamb-Chaplygin dipole, is used to investigate the conditions underÌýwhich stratified flow transitions to turbulence. NumerousÌýinvestigations have determined that a criticalÌýlength scale, known as the buoyancy length, plays a key role in the breakdown andÌýtransition to stratified turbulence. At this buoyancy lengthÌýscale, an instability unique to stratified flow, the zigzagÌýinstability, emerges. However investigations into sub-buoyancy length scales have remained unexplored. In this thesis we discover andÌýinvestigate a new instability of the Lamb-Chaplyin dipole that exists at the sub-buoyancy scale. Through numerical linear stability

analysis we show that this short-wave instability exhibits growth rates ÌýÌý similar to that of the zigzag instability. We conclude withÌýnonlinear studies of this short-wave instability and demonstrate thisÌýnew instability saturates at a level proportional to the cube ofÌýthe aspect ratio.