Vortical hot towers in a rapidly intensifying mature hurricane: observations and implications

Rapid intensification of tropical cyclones has become a focused area of research due to its potential threat to coastal regions. Asymmetric intensification mechanisms, such as hot towers and vortex Rossby waves, have been shown to aid in rapid intensification. In particular, vortical hot towers have been demonstrated to aid cyclogenesis, but have yet to be studied as a rapid intensification mechanism in hurricanes (having completed genesis). The objective of this study is to elucidate the characteristics, evolution, buoyant energy sources, and relevant vorticity generation for observed vortical hot towers during a rapid intensification period of a mature hurricane.

This study utilizes an extensive observational dataset collected during repeated dual-aircraft penetrations of Hurricane Guillermo (1997) on 2 August 1997 over a 6 h period. Estimates of the vertical velocity, vertical vorticity, and horizontal convergence are derived from 10 unique three-dimensional dual-Doppler wind fields of the inner core with horizontal spatial resolution of 2 km, vertical resolution of 0.5 km, and a temporal resolution of ~35 min. The azimuthal distribution and evolution of transient convective cells is determined from animated radar imagery. The buoyant energy sources and vorticity generation for each hot tower (regular and vortical) are determined from forward and backward air parcel trajectories derived from the dual-Doppler wind fields.

Preliminary results indicate the frequent collocation of anomalous vertical velocity and vertical vorticity extending from the boundary layer to upper levels of the troposphere, suggesting the existence of vortical hot towers. Both classic hot towers and vortical hot towers appear to reside in the eyewall during rapid intensification, along with a persistent wavenumber-one structure with an enhanced vertical velocity in the downshear left quadrant. A census of air parcels passing through the vortical hot towers will be performed to locate buoyant energy sources and used to elucidate how the enhanced vorticity of the parcels is generated. A synopsis of our preliminary results will be presented at the conference.