Tropical Cyclone Tilts Under Vertically Varying Background Flows: Preliminary Results Based upon TCM4 Simulations

Abstract

The characteristics of tropical cyclone (TC) tilts under vertically varying background flows were preliminarily examined in this study based on numerical simulations with the Tropical Cyclone Model version 4 (TCM4). The tilt magnitudes presented a linearly decreasing tendency in the simulation with the environmental wind speed vertically varying throughout the troposphere and in the simulation with the vertical wind shear concentrated in the lower troposphere, while the vortex tilt showed a linearly increasing tendency in magnitude in the simulation where the vertical shear was concentrated in the upper troposphere. The change in tilt magnitude was found to be related to the evolution of the penetration depth near the eyewall. When the shear was concentrated in the lower troposphere, the vortex tended to tilt downshear right during the early integration and underwent more precession processes. When the shear was concentrated in the upper troposphere, the vortex rapidly tilted downshear left during the early simulation and vortex precession was less frequently observed. The storms simulated in all experiments were finally in downshear-left tilt equilibrium.