Observational Evidence for Predictions of Tropical Cyclone Propagation Relative to Environmental Steering.
Theories of vortex motion due to the variations of the Coriolis parameter and environmental vorticity are compared to observations of tropical cyclone motion relative to computed `steering flows' using previously published composite data. The composite results are manipulated to obtain a vector quantity for the difference between tropical cyclone motion and steering, and this vector difference is termed `propagation.' The properties of these propagation vectors within various composite data stratifications provide tentative support for nonlinear numerical results such as: (i) the general magnitude and direction of the -induced propagation; (ii) the dependence of such propagation on the outer-wind strength of the tropical cyclone; and (iii) the dependence of such propagation on the direction of the environmental vorticity gradient. Ambiguities in the composite data are discussed with respect to linear and nonlinear theories of tropical cyclone propagation, and several new composite data stratifications are suggested to facilitate detecting individual propagation-inducing processes.