Classification of Arctic Cyclones Based on Their Intensification Mechanisms

Abstract We present a systematic, year-round classification of Arctic cyclones (ACs) based on their intensification mechanisms and identify three distinct types. Type I is characterized by weak diabatic heating, weak low-level baroclinicity, and weak upper-level forcing. Type II exhibits strong upper-level forcing and strong diabatic heating, combining the features of type-B and type-C midlatitude cyclones. Type III is characterized by strong low-level baroclinicity. The three AC types differ in intensity evolution and structural characteristics. Type I has the weakest mean intensity and intensification rate, whereas type II shows the strongest. Both type II and type III display a westward vertical tilt and a low-level dominant vorticity structure during early intensification but evolve into a more upright, upper-level dominant structure later. Although type III shares strong baroclinicity with type-A midlatitude cyclones, its vertical tilt evolves over time, in contrast to the vertical phase locking associated with the baroclinic modal growth of type-A midlatitude cyclones. Type I represents a unique subset resembling isolated, barotropic monopole vortices with an upper-level dominant vorticity structure throughout development. The three AC types also exhibit distinct spatial distributions. Type II tends to intensify over the southern Nordic seas with a high atmospheric river occurrence. Type III primarily strengthens over the northern Nordic seas and along the Arctic frontal zone, while type I preferentially intensifies over the central Arctic. These distributions suggest that AC intensification mechanisms are closely tied to local environmental conditions. Additionally, our analyses indicate that some tropopause polar vortices are an integral part of an intensifying AC, while some are generated by a decaying, cold-core AC. Significance Statement Arctic cyclones are the primary storm systems in the Arctic. This study identifies three types of Arctic cyclones based on their development mechanisms. Type II is characterized by strong upper-level forcing and strong diabatic heating (including latent heating from condensation and freezing). Type III is characterized by a strong temperature gradient near the surface. In contrast, all three development mechanisms are weak in type I. The three types of Arctic cyclones (ACs) are characterized by different intensity and structural evolutions and have different geographic distributions. Type II tends to intensify over the southern Nordic seas, type III preferentially strengthens over the northern Nordic seas and coastal Siberia, whereas type I primarily intensifies over the central Arctic Ocean. The classification provides a conceptual framework for understanding the development mechanisms and evolutionary processes of Arctic cyclones.