Vortex axial-symmetrization characterized by fractal dimension

Abstract

The vortex axial-symmetrization is an important dynamical process affecting tropical cyclone track change, and it is identified by previous work, up to now, in terms of vorticity fields rather subjectively. Two-dimensional simulations whose integration time is 48 h using a quesi-geostrophic non-divergence barotropic vorticity equation model are performed. The evolutional processes from an initial non-axial-symmetric vortex to the final axial-symmetric vortex are produced. Fractal dimension DB of the perimeter of the vortex is calculated hourly based on the model output data. The results show that fractal dimension can be used to characterize the vortex axial-symmetrization objectively. Based on DB calculated, the correction coefficients CRD and CVD are calculated to be CRD=-0.70 and CVD=-0.75. They each have a significant correction. Here CRD denotes the correction coefficient between DB and Rm being TC scale parameter, and CVD denotes the correction coefficient between DB and Vmax being tropical cyclone intensity parameter. The relation between the vortex axial-symmetrization and the tropical cyclone parameters may be characterized. The results have potential applications in tropical cyclone forecasting.