Balanced Evolution of the Vortex Tilt of Simulated Tropical Cyclones in a Sheard Environment

Recent research has increasingly focused on the intensification of Tropical Cyclones (TCs) under conditions of moderate vertical wind shear. Both observational and numerical data have underscored the crucial role of vertical alignment in TC vortices for the intensification process. However, the key physical processes influencing the evolution of vortex tilt are still not clearly understood. This study investigated the vertical structural evolution of TCs subjected to constant, moderate vertical wind shear. Similar to the wave-mean flow decomposition in the work of Reasor and Montgomery (2001), the tilted TC structures in our study are decomposed into an axisymmetric component and a superimposed asymmetric component. The potential vorticity inversion system with nonlinear balanced (NLB) constraints was conducted to investigate the balanced characteristics of asymmetric components. The results indicate that the wave-1 balanced asymmetric structures can account for the wave-1 asymmetric structures and the evolution of tilt in the simulated TCs. We further confirmed that in full-physics simulations, the wavenumber-one structures closely resemble the properties of Vortex Rossby Waves (VRWs). Similar results can be attained by employing statistical analysis to extract the principal wavenumber-one asymmetric structures. This study suggests that the dynamics of the wavenumber-1 vortex Rossby waves play an important role in the regulation of the physical processes associated with the evolution of the vertical structure of simulated tropical cyclones in sheared environment.