The Eady model describes quasi-geostrophic baroclinic instability in a uniformly stratified layer with constant vertical shear, zero interior potential-vorticity gradient, and two rigid horizontal boundaries.
Eady instability arises when counterpropagating Rossby waves localized on the upper and lower boundaries phase-lock and amplify one another.
A boundary Rossby wave is supported by a buoyancy or potential-temperature anomaly on a rigid horizontal boundary. Its intrinsic propagation opposes the local basic flow in the Eady model.
Adding linear damping to one boundary of the Eady model makes the two boundary-wave phase speeds complex and can destabilize modes that were neutral without damping.
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The Eady model refers to a theoretical framework used in meteorology to describe the behavior of atmospheric flows, particularly in the context of large-scale geophysical fluid dynamics. Named after Sir John Eady, who developed the model in the mid-20th century, it provides a simplistic representation of baroclinic instability in a two-layer system of the atmosphere.