Mechanisms and Structure of Intense Summer Arctic Cyclones Compared to Mid-Latitude Cyclones

Escalating threats posed by intense summer Arctic cyclones (ISACs) to socioeconomic activities in the Arctic necessitates a comprehensive understanding of their intensification and structural evolution mechanisms. This study employs a cyclone-center synthesis method and diagnoses the evolution of ISACs before and after their peak development phase. We find an annual average of four ISACs impacting the Arctic: 52.3% form in mid-latitude regions, and 90.9% reach peak intensity after intruding into the polar region. The frequency of ISACs show no significant trend from 1980 to 2022, whereas the duration of ISACs maintaining extreme intensity in the polar region increases significantly by 2.7 hr per decade. Before peak development phase, the ISACs develop similarly to mid-latitude cyclones. Upper-level warm temperature advection, mid-level positive vorticity advection and diabatic heating (DIA) collectively enhance near-surface vorticity. Adiabatic cooling throughout the troposphere induced by strong upward motion acts as a counterforce. During their intersection with upper-level tropopause polar vortices (TPVs), ISACs exhibit a more pronounced and sustained vertical structure than that of mid-latitude cyclones. Such structure of ISACs is characterized by a stratospheric warm core due to adiabatic heating and descent, and a tropospheric cold core resulting from adiabatic cooling and a lack of convective DIA. After ISACs overlap with TPVs, the upper-level circulation of ISACs can be sustained after the peak development phase. Compared to mid-latitude cyclones, the persistence of the upper-level circulation and interactions between ISACs with TPVs are found in this study to be a key factor contributing to the extended lifetime of ISACs.