On the basic dynamics of regional cyclogenesis

Abstract

This paper investigates the dynamics of regional cyclogenesis from the perspective of local instability of a zonally inhomogeneous baroclinic jet streak in a two-layer quasi-geostrophic beta-plane channel model. When such a representative jet streak is embedded in a background uniform vertical sheat UT, there are both local and global unstable normal modes. In the absence of such a background shear (UT=0), only the local modes are unstable. The shorter the jet is, the fewer local modes would there be. A local mode consists of a group of dominant waves that jointly give rise to a maximum local energy downstream of the jet core. Its existence is independent of the cyclical boundary condition. The growth rate of a local mode diminishes rapidly when the constant part of the basic zonal wind U0 is increased. A global mode, on the other hand, largely consists of a single wave and its growth rate is much less sensitive to U0. These properties are qualitatively similar to those in the WKB solution. -from Authors