The relationship between the linear baroclinic instability of zonally asymmetric mean flows and nonlinear eddies in a dry idealized GCM

Interactions between stationary waves and baroclinic eddies are central in establishing zonally confined extratropical storm tracks, such as those of the northern hemisphere. Because of the complexity of this eddy-mean flow interaction, simple heuristics such as relating transient eddy kinetic energy to the local Eady growth rate are often used to reason about storm tracks, even though the generality of these relationships is unclear.

Here, we revisit the problem of linear baroclinic instability for zonally asymmetric mean flows generated by a dry idealized general circulation model (GCM) to closely examine the relationships between properties of the mean flow, linear waves, and nonlinear eddies. In a series of GCM simulations, properties of the zonal asymmetry of the mean flow are varied, and the linear stability of the flow is assessed. This allows a systematic examination of the relationship between the spatial structure of (i) the Eady growth rate of the time-mean flow, (ii) the eddy kinetic energy of the most unstable linear waves, and (iii) the eddy kinetic energy of the nonlinear GCM simulation. In addition, we examine the extent to which the zonal asymmetry of the mean flow modifies the length and time scales of the linear waves relative to those of a corresponding zonally symmetric mean flow.