Abstract
High resolution simulations of idealized baroclinic wave life cycles on both the f-plane and the β-plane are performed. The anelastic, nonhydrostatic equations are employed in these analyses and motions are assumed dry adiabatic and inviscid, apart from a weak horizontal diffusion. Cyclogenesis is documented in considerable detail and features the formation of an occlusion with spiraling temperature contours that cuts off completely from the main warm air mass late in the life cycle in all cases. Thereafter, the occlusion develops independently of the remaining warm–cold frontal cusp and decays by becoming zonally elongated. Later redevelopment involving reorganization of the occlusion into the more nearly circular shape that obtains at the time of cut-off can reoccur on the f-plane leading to an oscillatory life cycle.
Features of the simulated synoptic scale vortices that are in common with observed cyclones are the comma-shaped vertical velocity pattern, the spiraling temperature and vorticity patterns at the surface, and mesoscale bands of rising air within the occlusion and along the comma tail. The similarity of our results with a variety of observations suggests the potential for dry dynamics alone to explain many of the mesoscale features of actual cyclogenesis events. Many such features are, therefore, plausibly understood as being forced by synoptic scale processes. Within the context of primitive equations dynamics the β-effect is shown to enhance the asymmetry between surface frontal intensities and to cause the occlusion to develop farther north than is characteristic on the f-plane.
