Accumulation, local instability, and the generation of atmospheric low frequency variability

The generation of low frequency variability in the extra-tropical atmosphere remains an important area of research in dynamic meteorology. While the upscale cascade of energy from synoptic-scale eddies associated with baroclinic instability is vital to the generation of extra-tropical low frequency variability, evidence suggests that intrinsic instabilities of the planetary scale flow are also of importance. In this presentation, various paradigms for the instability of the planetary scale flow will be highlighted, emphasizing the accumulation of wave energy in strongly convergent group velocity fields and the emergence of local instabilities to zonally varying barotropic and continuously stratified flows. Emphasis will be placed on those instabilities that lead to observationally relevant structures, including blocking onsets, as well as on observational identification of similar instability mechanisms in the atmosphere.