All-season analysis of extratropical and Arctic cyclones over the Northern Hemisphere oceans during 1940-2024
Bibliographic record
Abstract
[1]¿p#1 Extratropical and Arctic cyclones regulate mid-to-high-latitude climate through the transport of heat, moisture, and momentum, yet their long-term behavior beyond the well-studied winter and summer seasons remains poorly understood. Using an 85-year (1940–2024) cyclone climatology derived from ERA5 reanalysis, we identify 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 and exhibit lengthening lifespans and trajectories. In the North Atlantic, cyclone paths have lengthened in winter; genesis has risen in spring, and storm lifespan has lengthened in autumn. In the North Pacific, tracks also have lengthened in winter, while autumn storms have become larger, longer lived, and farther traveled. 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 the 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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".