Search

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. [ABSTRACT FROM AUTHOR]

Two 1-km Weather Research and Forecasting model simulations of the rapid intensification (RI) periods of hurricanes Ike (2008) and Earl (2010), under low and high wind shear respectively, are performed to evaluate mechanisms linked to the initiation and maintenance of RI. Despite similar simulated intensification time series, the exhibited hydrometeor characteristics differ between the two cases since Ike possesses less asymmetry and less vigorous convection than Earl. An objective method to quantitatively estimate the radius of maximum wind (RMW) with respect to height is introduced for quantifying the primary circulation character of each storm, permitting analysis of where heating is most efficient for driving warm core growth and subsequent intensification. Following eye development in each, diabatic heating remains embedded within the RMW. Earl's RI onset coincides with an absolute maximum in diabatic heating occurring within the RMW, while Ike possesses relatively less diabatic heating inside the RMW throughout and lacks an absolute peak associated with RI. The majority of diabatic heating within the RMW of both cases occurs at subfreezing temperatures, indicative of the importance of clouds associated with ice processes in these RI simulations. Earl's diabatic heating peak is tied to a maximum in convective burst activity residing within the RMW. Earl's preference for more sparse but intense convection is associated with increased sea surface temperatures, surface heat fluxes, moisture convergence, and near-surface equivalent potential temperature relative to the broader, weaker convective character in Ike. [ABSTRACT FROM AUTHOR]