A Theory of Deep Cyclogenesis in the Lee of the Alps. Part I: Modifications of Baroclinic Instability by Localized Topography

The theory of cyclogenesis in the lee of the Alps presented by Speranza et al. in Part I is reexamined here (Part II) in the context of models dealing with finite amplitude topography. This generalization leads to the specification of the limits of validity of the approximations made in Part I and, at the same time, allows us to calculate the stability properties and normal mode structure of the model atmosphere with realistic topography. The effects of finite slope and finite geometrical height of the mountain are considered separately and their relative importance is evaluated. In the case of a three-dimensional obstacle with an idealized shape simulating the Alps, the modifications induced by the orography on the free, baroclinically unstable modes show essentially the same features observed in numerical experiments, including the orientation of the dipolar structure in the pressure perturbation across the mountain.