Diagnosis of Arctic Cyclone Structure and Comparison with Midlatitude Cyclones
Using the ERA5 reanalysis and an Arctic cyclone (AC) track dataset with more than 10,000 AC tracks, we examined the similarities and differences between Arctic cyclones and midlatitude cyclones, regarding how the cyclone characteristics change as they propagate into the Arctic, and how Arctic cyclones developing in the Arctic differ from those originating from the midlatitudes. Three groups of cyclones are examined, i) Arctic cyclones forming in the polar region (≥70N); ii) Arctic cyclones originating from the midlatitudes (<70N); and iii) midlatitude cyclones that later propagate into the Arctic.
More ACs form in the polar region than in midlatitudes in all seasons. Regarding seasonality, ACs of the polar origin occur most frequently in boreal winter, mainly due to frequent cyclogenesis over the Nordic Seas. ACs of the midlatitude origin occur most frequently in boreal summer, and meanwhile frequent cyclogenesis occurs along Arctic frontal zones in summer. As cyclones propagate from midlatitudes into the Arctic, their vertical tilt is reduced, and they become more symmetric. Arctic cyclones are, on average, weaker than midlatitude cyclones in terms of sea level pressure and undergo strong intensification less frequently.
Composite analysis shows that ACs are characterized by a warm-core structure in the lower stratosphere, consistent with previous studies. It is related to both adiabatic warming and horizontal temperature advection. The latter process enhances the warm core in summer but weakens it in winter. The diagnosis using the cyclone phase space suggests that typical Arctic cyclones begin their life cycle with an asymmetric cold-core structure in the troposphere and evolve into a more symmetric structure with a weaker cold core at the later stage.
