Characterization of the Dynamical Role of Convection in two Simulated Episodes of Rapid Intensification

Recently much attention for study of tropical cyclone intensification has been focused on the importance of diabatic heating occurring within the radius of maximum winds (RMW) due to the increased inertial stability of this region aiding in warm core development. Prior works focusing on the RMW importance in terms of diabatic heating location have been typically based upon highly-idealized simulations of tropical cyclone-like vorticies. Here, an objective algorithm for determining an estimated position of the three-dimensional RMW is applied to 1-km simulations of rapid intensification (RI) by the Weather Research and Forecasting (WRF) model of Hurricanes Ike (2008) and Earl (2010) under low and high ambient wind shear respectively. We seek to determine how precipitation processes within the RMW evolve relative to rapid intensification timing in three-dimensional simulations of realistic TCs.

The 3-D RMW position can be used for an analysis framework to evaluate how various fields related to diabatic heating vary over time. The temporal evolution of vertical motion and diabatic heating within the RMW is compared prior to and following RI, revealing increased convective activity preceding RI onset for each TC. To further isolate contributions towards the diabatic heating within the RMW, a three-dimensional analysis of individual updrafts is undertaken to determine their relative contributions towards diabatic heating. Such updrafts can be grouped according to their maximum height, thus allowing for classification into approximate convective regimes (e.g. shallow cumulus, cumulus congestus, deep convection, and convective bursts) and the importance of such modes to be evaluated. Earl's RI is linked predominantly to increased vertical mass and moisture fluxes associated with convection penetrating the tropopause while for Ike the majority of these fluxes are associated with convection of lesser vertical extent.