The relationship between the wintertime north Atlantic oscillation and blocking episodes in the north Atlantic
Bibliographic record
Abstract
Abstract A systematic examination of the dynamical relationship between the North Atlantic Oscillation (NAO) and atmospheric blocking episodes in the North Atlantic during winter is undertaken. Employing the blocking criteria, as defined by Tibaldi and Molteni (1990), we first establish a statistical relationship, through compositing and linear regression analysis, between the two phenomena. The results show that the frequency of blocking formations in the North Atlantic region is sensitive to the phase of the NAO. Sixty‐seven percent more winter blocking days are observed during the negative than the positive phase of the NAO. The lifetime of blocking episodes is also sensitive to the phase of the NAO. When the NAO is in the negative phase, the distribution of the length of blocking varies considerably. The average length of blocking during the negative phase is about 11 days, which is nearly twice as long as the 6‐day length observed during the positive phase of the NAO. The NAO accounts for about 30% of the variation in the wintertime North Atlantic blocking episodes. We propose a conceptual model that strengthens the statistical association and offers an explanation for a dynamical connection between the occurrences of blocking and the NAO in the North Atlantic. Application of a low‐order theoretical model by Charney and DeVore (1979) and an analysis of Northern Hemisphere observed surface temperature suggest that the NAO‐related difference in blocking frequency and persistence are associated with changes in the zonally asymmetric thermal forcing which, to a large extent, is determined by the phase of the NAO. For the negative phase of the NAO, the distribution of the surface air temperature anomaly is the distinctive ‘warm ocean/cold land’ pattern related to the resonance forcing of topography and creates a dynamical environment favourable for the formation and persistence of blocks. For the positive phase of the NAO, on the other hand, the distribution of the surface air temperature anomalies is the distinctive ‘cold ocean/warm land’ pattern, which reduces or destroys the resonance forcing of topography and is unfavourable for the development and persistence of blocks. Copyright © 2001 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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".