A case study of cyclogenesis using a model hierarchy

It is universally agreed that cyclogenesis in midlatitudes occurs through baroclinic conversion of the potential energy available from an initial state. The mechanical process by which that conversion takes place is a perennial subject of discussion. At least as far back as the 1950s, it was recognized that in any practical forecast problem, the initial condition is influential. Observational research continues to confirm the prevalence of tropopause-level perturbations preceding surface cyclogenesis. The observations also suggest that the growing disturbances have time-varying vertical structures. Relating these observations to the classical linear theory of baroclinic instability is not immediately obvious since, in the latter, the precise form of the initial condition is not important, and the theory predicts cyclogenesis with a fixed-in-time vertical structure. These differences between theory and observations are but a few of the many that have been recognized and treated in modified theories of baroclinic instability. We attempt herein to draw a closer connection between the modified theories and observations by performing a case study using a hierarchy of models of decreasing complexity.