Favorable environments for explosive cyclogenesis in a modified two-layer Eady model

Abstract

A modified two-layer Eady model is used to find favorable environments for explosive cyclogenesis by examining baroclinic instability of both short and long waves. The model includes Ekman dissipation and low-level sensible heating, and allows both static stabilities and vertical shears to be different but constant in each layer. It is found that an enhanced low-level shear, a reduced low-level static stability, a relatively large upper-level static stability, and an appropriate height of the interface are favorable for the short-wave development, and that an enhanced upper-level shear and a relatively small upper-level static stability are favorable for the long-wave development, while having opposite effects on the short wave. A small Ekman dissipation is favorable for the development of both waves. Newtonian sensible heating does not directly enhance the development of both waves. A favorable environment for explosive cyclogenesis may not be expressed by a single parameter, but rather by a combination of baroclinic instability with several parameters which contribute collectively to the development of both short and long waves. The relative phase of these waves also plays an important part: the development is enhanced when the surface cyclone is ahead of the upper level wave trough by 1/4π. DOI: 10.1111/j.1600-0870.1987.tb00301.x