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 during October–April to detect ETCs during 1950–2023 over 22ᵒ-80ᵒN. The algorithm is unique in that 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 various characteristics over all cyclone-impacted areas rather than just ETC’s central locations. Each ETC characteristic except for travel velocity has relative maxima over the core oceanic storm track regions throughout all months, while maxima for ETC velocity exists over the eastern portions of Asia and North America. Furthermore, a strong relationship exists between ETC frequency and its standard deviation, with higher frequencies corresponding to higher variability. In contrast, regions and months with higher frequencies correspond to lower variability in intensity, area, lifespan, and velocity. A trend analysis reveals a zonal shift and slight weakening of the North Pacific storm track and a poleward shift and strengthening of the North Atlantic storm track, both extending to the surrounding land regions. 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, while multidecadal variability reduces the robustness of the trends, particularly for ETC lifespan.