Spiral rainband propagation: Vortex-Rossby waves vs. tropical squall lines

Three hypotheses have been proposed to explain the properties of spiral rainband propagation. Each hypothesis views spiral rainbands as 1) internal gravity waves that are generated from the rotating convective asymmetries in the eyewall region; 2) vortex-Rossby waves that emanate radially outward from the eyewall along the sharp negative potential vorticity gradient; or 3) tropical squall lines that maintain their structures through mechanical lifting along spreading, dense cold pools. Depending on how spiral rainbands are characterized, their propagation properties are significantly different. This study will examine how spiral rainbands propagate in high-resolution, full-physics numerical simulations of Hurricane Bill (2009) and make comparisons to previous hypotheses.