Detection of past and future atmospheric circulation changes over the North Atlantic region with the help of an automatic circulation type classification
Notice bibliographique
Résumé
Future projections of the atmospheric circulation over the Northern Hemisphere high latitudes, especially the North Atlantic, have high uncertainties and some of the projected changes are opposed to circulation changes that have been observed since the 2000s. In this thesis, we focus on three particular aspects of the past and projected future summertime atmospheric circulation over the broader North Atlantic region. First, we analyse whether the 2007-2012 summertime anticyclonic anomaly over the Beaufort Sea, the Canadian Arctic Archipelago, and Greenland might rather be due to global warming or to the internal variability of the atmospheric circulation by putting it in perspective with the circulation variability over the last 150 years given by five reanalysis datasets. Then, this analysis is extended for the future circulation projected towards 2100 by CMIP3 and CMIP5 General Circulation Models (GCMs) over Greenland. Finally, we evaluate the impact of the uncertainties of the future atmospheric circulation projections on the mitigating or enhancing influence of the summertime circulation changes on temperature and precipitation over Europe. We use an automatic circulation type classification to analyse in detail the atmospheric circulation changes by grouping similar daily SLP (mean sea level pressure) or Z500 (500 hPa geopotential height) fields into homogeneous circulation types. It appears that the choice of the index, on the basis of which the days are grouped together, strongly influences the characteristics of the circulation types and the kinds of circulation changes that can be detected. In comparison with Euclidean distance and pressure gradient-based indices, correlation-based indices, especially the Spearman rank correlation, are the most suitable indices when focusing on the circulation pattern. Over the Arctic region, four periods with circulation anomalies similar to that of 2007-2012 (i.e. a summertime anticyclonic anomaly over the western Arctic region) have been detected over the last 150 years, despite a higher uncertainty of the circulation given by the reanalyses due to the scarcity of observational data before 1940. Nevertheless, the 2007-2012 anomaly appears to be exceptional and several connexions with other variables, such as the North Atlantic Oscillation index and sea ice loss, suggest that it could be part of a major climatic anomaly extending beyond the Arctic region. However, the occurrence of similar periods in the past and the influence of several external and internal forcings do not allow us to attribute it to global warming. The future summertime atmospheric circulation projected by GCMs over Greenland confirms this conclusion. In fact, no significant circulation pattern changes are simulated towards 2100, besides a generalised Z500 increase caused by the projected warming. Since GCMs are able to simulate atmospheric circulation changes over other regions and since the atmospheric circulation itself is influenced by other variables, such as sea ice or snow extent, which are already impacted by long-term changes, we conclude that the 2007-2012 anomaly could rather be attributed to the internal variability of the climatic system. Finally, we evidence that projected future atmospheric circulation changes impact on the SLP and precipitation changes simulated over Europe towards 2100 for summer. Over north-western Europe, these circulation changes could mitigate the SLP decrease by around 50 % and cancel out the precipitation increase. Nevertheless, high uncertainties among the GCMs on the magnitude and even on the sign of these changes cast doubt on the reliability of these projections. On the other hand, future atmospheric circulation changes are not projected to affect significantly the warming and drying simulated for the next decades over the Mediterranean region and eastern Europe.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,002 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,003 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».