On the development of extratropical cyclones

Abstract Certain synoptic aspects of cyclone development in the lower troposphere are reviewed and two types identified. Type A comprises the well‐known amplifying frontal wave, which is known to produce kinetic energy through a reduction of the baroclinicity within its own domain. Type B is found to be initiated through a finite disturbance in the upper troposphere, and its intensification is accompanied by an augmentation of the baroclinicity and import of kinetic energy, mainly from the jet‐stream region. The energy structures of two storms are described, one being a plain type B case, and, the other representing a type B development modified through the presence of strong fronts. The dissipation of kinetic energy in the surface air is computed and found to constitute an effective brake on cyclone development.