An analysis of the environmental energetics associated with the transition of the first South Atlantic hurricane

This study presents the first analysis of the energetics associated with a hybrid cyclone's transition in the Southern Hemisphere, Hurricane Catarina (March 2004). Catarina has earned a place in history as the first documented South Atlantic hurricane, but its unusual tropical transition is still poorly understood. Here we show that Catarina's transition was preceded by marked environmental changes in the Lorenz energy cycle, with an abrupt shift from a baroclinic to a predominantly barotropic state. Such changes help to explain the unusual vortex's growth until its transition was completed. Although the vortex's energy flux is not explicitly calculated, a likely mechanism linking the environmental energetics with Catarina is the extraction of eddy kinetic energy from horizontal momentum and heat transfers within the through component of the blocking. The results advance the understanding of this rare event and suggest that the technique has a great potential to study transitioning systems in general.