Decoupling of Balanced and Unbalanced Motions and Inertia–Gravity Wave Emission: Small versus Large Rossby Numbers

Abstract

This paper provides a brief review of recent results on decoupling of fast [inertia?gravity wave (IGW)] and slow (vortex) motions at small Rossby numbers obtained in the framework of the geostrophic adjustment of localized perturbations. Special attention is paid to the IGW emission and its interpretation in the context of ?spontaneous imbalance.? Several mechanisms that lead to spontaneous IGW emission and, thus, to violations of fast?slow splitting at large Rossby numbers are reviewed: Lighthill radiation, symmetric/inertial instability, and ageostrophic shear (Rossby?Kelvin) instability. New results on the saturation of symmetric instability and on the existence of Rossby?Kelvin instability in continuously stratified fluid are presented.