CYCLOPs: a Unified Framework for Surface Flux-Driven Cyclones Outside the Tropics

Abstract

Cyclonic storms resembling tropical cyclones are sometimes observed well outside the tropics. These include medicanes, polar lows, subtropical cyclones, Kona storms, and possibly some cases of Australian East Coast Lows. Their structural similarity to tropical cyclones lies in their tight, nearly axisymmetric inner cores, eyes, and spiral bands. Previous studies of these phenomena suggest that they are partly and sometimes wholly driven by surface enthalpy fluxes, as with tropical cyclones. Here we show, through a series of case studies, that many of these non-tropical cyclones have morphologies and structures that resemble each other and also closely match those of tropical transitioning cyclones, with the important distinction that the potential intensity that supports them is not present in the pre-storm environment but rather is locally generated in the course of their development. We therefore propose to call these storms CYClones from Locally Originating Potential intensity (CYCLOPs). We emphasize that mature CYCLOPs are essentially the same as tropical cyclones but their development requires substantial modification of their thermodynamic environment on short time scales. Like their tropical cousins, the rapid development and strong winds of CYCLOPs pose a significant threat and forecast challenge for islands and coastal regions, and the effects of climate change on them should be considered.