Development of Intense Helicity and Convective Bursts in Hurricane Bonnie (1998)

Three-dimensional (3D) structures and evolution of helicity and vorticity generation under stronger vertical shear during the rapid intensity changes is examined using a 5-day simulation of Hurricane Bonnie (1998) with the finest 4-km resolution (Zhu et al. 2004). The model-simulated helicity distribution and magnitude are compared to those observed results by Molinari and Villaro (2008). After ensuring the similar helicity distribution to that of Molinari and Villaro (2008), we examined the 3D structures and evolution of helicity of Bonnie, and the developments of Bonnie's “convective bursts” (CBs). CBs in relation to convective available energy (CAPES), helicity, vertical wind shear (VWS), and relative vorticity generation during RI and vorticity couples in rainband were also investigated. It is found that on the effect of helicity and CAPE, convective bursts organized upscale to offset the influence of vertical shear and help maintain the vortex. In rainband, intense convective cells relevant to vorticity couplets produced by the tilting of vorticity generation spiralled into the eyewall to enhance the hurricane vortex.