The development of asymmetries in a three-dimensional numerical model of the tropical cyclone

Notable asymmetric features of an early experiment with a three-dimensional hurricane model (Anthes et al., 1971a) were spiral bands of convection and large scale asymmetries (eddies) in the outflow layer. Using an improved version of the model, the formation and maintenance of these features are described in greater detail in this paper. The spiral bands in the model are found to propagate cyclonically outward in agreement with bands in nature. The breakdown of symmetry into a chaotic pattern of eddies in the outflow region is shown to be the result of dynamic (inertial) instability, with the eddy kinetic energy derived from the kinetic energy of the azimuthal mean flow. This instability does not contribute to the overall intensification of the model storm, however.