The Role of the Radial Vorticity Gradient in Intensification of Tropical Cyclones

Abstract. The role of the radial vorticity gradient in tropical cyclone dynamics is explored through a low-order conceptual box model. Specifically, we look at stable-to-stable state transitions which may be linked to tropical cyclone intensification, dissipation, or eyewall replacement cycles. To this end, we identify two parameters of interest: the exponent of radial decline and sea surface temperature. We examine how variation in these parameters affect the stable states of the model and consider the behaviour of the system under time-dependent parameters. By externally forcing the exponent of radial decline and sea surface temperature we show the existence of rate-dependent behaviour in the model. These findings are brought together in a case study of Hurricane Irma (2017). The results highlight the role of the radial vorticity gradient in behaviour such as rate-induced tipping and overshoot recovery. They also show that a simple model can be used to explore relatively complex tropical cyclone dynamics.