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This analysis of cyclones over the northern hemisphere oceans reveal several significant relative trends (trend/climatology) around the Baltic Sea area. Notably this includes:
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Extratropical and Arctic cyclones play an important role in shaping climate, ecosystems, and human activities. These storms help move heat and moisture toward the poles and affect sea ice, ocean waves, coastal flooding, and marine transportation. While past research has mostly focused on changes in cyclones during winter and summer, much less attention has been given to the transitional seasons—spring and autumn. In this study, we analyzed long-term weather data from 1940 to 2024 to examine how cyclones over the Northern Hemisphere oceans have changed across all seasons. We found clear and important seasonal shifts. In the Arctic, spring cyclones are now stronger, last longer, and travel farther. In the North Atlantic, more cyclones are forming in spring, and autumn storms are lasting longer. Similar trends appear in the North Pacific, where autumn storms are becoming larger, longer-lived, and more wide-ranging. These changes are closely linked to the loss of Arctic sea ice. As ice retreats, the temperature contrast between the ocean and atmosphere increases, creating favorable conditions for stronger storm development. Our findings highlight the need for seasonal forecasts and climate models to pay more attention to spring and autumn cyclones—not just those in winter and summer.
Extratropical and Arctic cyclones regulate mid-to-high-latitude climate through the transport of heat, moisture, and momentum; however, their long-term behavior during spring and autumn seasons remains poorly understood. Using an 85-year (1940–2024) cyclone climatology derived from ERA5 reanalysis, we identified substantial seasonal and basin-specific shifts in Northern Hemisphere marine cyclone activity. Most notably, cyclone occurrence and intensity have significantly changed over the central Arctic Ocean, with winter storms becoming fewer but markedly deeper, and summer storms more numerous. Arctic cyclones in spring, previously under-investigated, have intensified (−0.31 hPa decade−1) and exhibit lengthening lifespans (+0.02 days decade−1) and trajectories (+29.44 km decade−1). In the North Atlantic, cyclone paths have lengthened in winter, genesis has risen (+0.73 decade−1) in spring, and storm lifespan has lengthened (+0.03 days decade−1) in autumn. In the North Pacific, tracks also have lengthened in winter, while autumn storms have become larger (+10.37 km decade−1), longer lived (+0.03 days decade−1), and farther traveled (+30.35 km decade−1). These observed cyclone changes are closely tied to the coupled responses from surface to upper-tropospheric levels. Pronounced sea ice loss coincides with enhanced lower-tropospheric baroclinicity (increased Eady growth rate) and a weaker upper-tropospheric potential vorticity gradient. Together, these adjustments favor stronger, deeper cyclones and facilitate their meridional propagation. Our results demonstrate that long-term climate change is reshaping Northern Hemisphere cyclone characteristics far beyond traditionally emphasized seasons. These findings highlight an urgent need for seasonal climate forecasts and long-term projections to give spring and autumn cyclones equal consideration alongside winter and summer extremes.
DOI: 10.1029/2025JD044894
Publication Date: 2026-03-12
