On Short-Wave Baroclinic Instability

The Physical process responsible for short-wave baroclinic instability (zonal wavenumbers>10) is examined by means of a linearized two-layer Eady model. The static stability is uniform but different in each layer and the wind shear is uniform throughout both layers. Analysis of the unstable growth rates reveals that the instability is associated with the delta function distribution of potential vorticity at one boundary and at the interface between the two layers. This interpretation complements the interpretation of the unstable modes of a multi-layer model by Staley and Gall (1977). However, the present analysis also demonstrates how the short- and long-wave baroclinic instabilities depend on the relative layer depths as well as on the jump in static stability between the two layers. The effect of a jump in zonal wind shear is shown to be analogous to a jump in static stability in the present model. Finally, some implications of modeling atmospheric flows by multi-layered models, exhibiting discontinuities in potential vorticity, are pointed out.