Asymmetric Eyewall Vertical Motion in a High-Resolution Simulation of Hurricane Bonnie (1998)

Reasor et al. (2004) examined the tilting of a vortex by shear and found that a damping mechanism intrinsic to the dry adiabatic dynamics suppresses departures from an upright state. This realignment occurs through projection of the tilt asymmetry onto two types of vortex Rossby waves: sheared vortex Rossby waves, in which the radial shear of the swirling flow axisymmetrizes tilt asymmetries, and a quasi-mode, or discrete, vortex Rossby wave that, in the absence of damping, causes precession of the upper vortex until it realigns with the lower one (thereafter undergoing repeated cycles of tilting and realignment). With damping, the vortex achieves a downshear-left equilibrium tilt. This paper examines the role of a damped quasi-mode in producing asymmetric vertical motions in a high-resolution simulation of Hurricane Bonnie (1998).