The causes, variability and behaviour in a warming world of the coldest winter-season Canadian temperatures and their associated Arctic air masses
Notice bibliographique
Résumé
The coldest surface temperatures in Canada are associated with arctic air masses. These air masses form during the snow-covered and low-sunlight environment of the high-latitude northwest in the winter. This is a region that has been experiencing intense localized surface temperature warming that has not been well captured by climate models. The purpose of this study is to examine the arctic air masses of the region in detail, the larger synoptic context of changes in temperature intensity across Canada in which they are embedded, their thermodynamic properties, and secular changes that they may be experiencing.Trends in temperature anomalies relative to a 30-year running mean were examined, a measure of changes in intensity separated from changes in the mean. Trends towards decreasing variability were found in the southwest and northeast during the winter and trends in increasing variability in the Prairies, southern Ontario and Quebec during mid-winter and in the Atlantic stations in the early-spring. However, no trends were found in the variability of the northwest meaning that even though temperatures inside arctic air masses are increasing, their intensity relative to the 30-year running mean has not been changing.Ninety-three arctic air masses were isolated, using the anomalies calculated relative to the 30-year running mean, and examined. They were found to be deep-layer cold-air damming events associated with an intense anticyclone in the lee of the Canadian Rockies. Using a thermodynamic budget, we find the primary formation mechanism to be diabatic, with cold-air advection playing a small role, counter-balanced by subsidence warming. Sublimation cooling from snowfall at the start of the formation is one of the diabatic processes playing a role. A secular trend toward deeper events was found and decreased radiative cooling during the event, possibly owing to increased cloudiness.In a case study of an intense and long-lived event in February of 1979, moisture was found to be a crucial component in maintaining the cold air. Ice crystals radiatively cool the layer in which they are embedded but settle gravitationally over time or are brought to the ground through subsidence. Moisture must be replenished by precipitation if the air mass is to continue cooling. Moisture transport into the event region is primarily from the upper-levels, 700 hPa, from cyclones in the Gulf of Alaska and from the north over the pole, where it precipitates and falls into the lower-levels.
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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 | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,002 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| 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 ».