Climatology, trends, and variability of cold-season northern hemisphere extratropical cyclone characteristics during 1950–2023 in ERA5

Understanding historical changes and variations of extratropical cyclones (ETCs) is crucial for contextualizing current and future ETC changes and their wide-ranging impacts. Here, we apply a modified tracking algorithm to hourly sea-level pressure data from the ERA5 reanalysis to detect ETCs during October–April 1950/51–2023/24 over 22°–80° N. ETC statistics are recorded at all grid cells encompassed by an ETC’s outermost isobar, thus providing spatial visualizations regarding the climatology, variability, and trends of ETC’s frequency, intensity, area, lifespan and velocity over all cyclone-impacted areas rather than just ETC’s central locations. All ETC characteristics exhibit a canonical pattern with high (low) values over the North Pacific and North Atlantic (Eurasia and North America) except for travel velocity which has maxima over East Asia and eastern North America. A trend analysis reveals a westward shift of the North Pacific storm track particularly during November and a poleward shift and strengthening of the North Atlantic storm track only in January-March, both extending to the surrounding land regions. Regional time series reveal that a continuation of trends for approximately one century could result in historical yearly variations being exceeded. Substantial inter-month variations exist for the trends in each ETC characteristic and the trends are only significant during certain months of the cold season. Yet, long-term changes in baroclinicity generally align with and provide a physical context to shifts in the oceanic storm tracks, particularly over the North Atlantic. Baroclinicity changes over the North Pacific are weaker than the North Atlantic.