The Intensity-dependence of Tropical Cyclone Intensification in a Simplified Energetic System and a Full Physics Model

Abstract:

Several recent studies based on best track data for tropical cyclones (TCs) over the North Atlantic revealed a strong dependence of the TC intensification rate (IR) on TC intensity. The TC IR shows a maximum (i.e., most rapid intensification) when the TC intensity reaches about 35 - 40 m s^-1. Physically, this intensity-dependence has been explained in terms of the inner-core inertial stability and the decreased potential for a TC to intensify as it approaches its maximum potential intensity (MPI). Here, we propose a new simplified dynamical system based on TC energetics. For this purpose, the TC system is considered as a Carnot heat engine as in earlier theoretical studies, and formulated on the grounds of major energy production and dissipation processes. This offers a way to explain the IR behavior of TCs in terms of its sensitivity to the physical processes involved, and to derive a physically-based relationship between TC intensification and intensity. This relationship is consistent with observations, and in quantitative agreement with that gained from empirical relations in an alternative dynamical system proposed by DeMaria(2009), which has been formulated analogously to the logistic growth equation (LGE). Results from idealized full-physics model simulations confirm the validity of several key assumptions implicitly involved in the simplified dynamical system and the intensity-dependence of the TC IR as well.