Varied pathways for simulated tropical cyclone rapid intensification. Part II: Vertical motion and cloud populations

Abstract

Differences in the vertical velocity characteristics associated with various cloud populations are evaluated for two simulated cases of tropical cyclone (TC) rapid intensification (RI) under varying wind shear. Within the radius of maximum wind (RMW), preceding RI in the low‐shear TC (hurricane Ike of 2008) increased updraught magnitudes for the top 1% of the distribution at 7 km occur, while in the high‐shear scenario (hurricane Earl of 2010) RI is led by increased updraught magnitudes of the top 1% of the distribution at 12 km. Three‐dimensional analyses of individual updraughts relative to their peak altitude enables direct quantification of processes associated with shallow cumuli, cumulus congestus, deep convection failing to penetrate the tropopause, and convective bursts (CBs). Mean profiles for each convective regime reveal positive contributions in certain variables of each updraught variety towards RI with positive diabatic heating, absolute vorticity, and moisture convergence roles.Within the RMW, CBs are shown to be the primary diabatic heating and vertical mass and vapour flux contributors in both simulations, while Ike includes secondary contributions from deep convection and congestus in addition to noteworthy diabatic heating from apparent stratiform processes that act to spin up the mid‐level vortex. Inner‐core moisture convergence has divided contributions from shallow cumuli, cumulus congestus, and CBs. CBs act to enhance potential vorticity to the greatest amount and over the deepest vertical layer at low levels. The simulation results overwhelmingly support the aggregate importance of vertically developed deep convection and its associated ice processes to the initiation and maintenance of RI.