Abstract
Sutcliffe's theory of development is reviewed and extended, with particular reference to cyclonic development at sea level. It is shown that cyclogenesis results from an unbalance, in the layer below the level of non-divergence, of the vorticity advection and the Laplacian of certain thermal quantities. It is suggested that cyclogenesis results not from the release of an infinitesimal perturbation by a dynamically unstable state, but rather from the release of some kind of instability by finite perturbations which can be identified with the wave-shaped motion patterns in the middle and upper troposphere.
