Localized anomalies, Rossby wave-guides and baroclinic instability

One paradigm for extratropical cyclogenesis is the approach of an upper-level isolated potential vorticity (PV) anomaly toward a surface baroclinic zone (sic. Rossby wave-guide). However the upper-level anomaly itself has usually either evolved from, or is located contiguous to, the upper-level Rossby wave-guide that is aligned along the extratropical jet stream.

Here two complementary theoretical studies are undertaken of the nature of baroclinic development in the presence of all three-ingredients (i.e. two Rossby wave-guides and a PV anomaly). The first setting is that of the standard two-dimensional linear Eady problem modified to include an interior vertically-localized PV distribution, and the second is the non-linear evolution of a baroclinic jet under the influence of a localized upper-boundary anomaly again in a Eady-like configuration.

Consideration is given to the sensitivity of the development to the scale, strength and location of the anomaly relative to the Rossby wave-guides. The results shed light on the dynamics of super-exponential growth-rates, "optimal" perturbation structures, and the relative importance of interior-tropospheric as opposed to tropopause-level anomalies.