Tropical-cyclone intensification: Part I: The role of the boundary layer

This talk compares three paradigms for tropical-cyclone intensification, focusing on a new paradigm described in a series of recent papers with colleagues S. Nguyen, H. Bui and G. Thomsen. The new paradigm views the intensification process as intrinsically asymmetric and dominated by deep convective vortex structures. These convective structures, or “vortical hot towers”, exhibit a degree of randomness that has implications for the predictability of asymmetric features of the developing storm on the convective scale. The vortical hot towers possess local buoyancy relative to the azimuthally-averaged virtual temperature field of the warm-cored vortex. Using an idealized, three-dimensional, non-hydrostatic numerical model, we show that from an axisymmetric viewpoint, the spin-up of the inner core is associated with the convergence of absolute angular momentum in the boundary layer, where this quantity is not conserved. Observational evidence in support of this new paradigm will be presented.