A Dynamically Based Climatology of Subtropical Cyclones that Undergo Tropical Transition in the North Atlantic Basin

AbstractSubtropical cyclones (STCs) derive a considerable portion of their energy from baroclinic and diabatic processes. The opportunity to investigate the roles of baroclinic and diabatic processes during the evolution of STCs from a potential vorticity (PV) perspective motivates this study. The roles of baroclinic and diabatic processes during the evolution of STCs are determined by calculating three PV metrics from the 0.5° NCEP Climate Forecast System Reanalysis dataset. The three PV metrics quantify the relative contributions of lower-tropospheric baroclinic processes, midtropospheric latent heat release, and upper-tropospheric dynamical processes during the evolution of individual cyclones. An evaluation of the three PV metrics, as well as the sign of the upper-tropospheric thermal vorticity, during the evolution of individual cyclones is used to devise an objective STC identification technique and construct a 1979–2010 climatology of North Atlantic (NATL) STCs that undergo tropical transition.An i...