A climatology of North American air masses and their extremes in Montreal, Quebec
Bibliographic record
Abstract
Air masses are a fundamental quantity in both weather and climate. Extremely warm air masses in the extratropical latitudes are of interest because of their potential role in heavy precipitation. Our goal is to use 850 hPa equivalent potential temperature theta_e to provide a climatology of air masses in North America, and their extremes in Montreal, Quebec. A monthly climatology of 850 hPa theta_e is presented for the 33-year period between 1979-2011. A statistical analysis shows that theta_e has significantly increased in the Montreal region during the period in question. No trend in the variance was detected. 40 extreme theta_e events were selected in Montreal by choosing the top ten cases for each season (DJF, MAM, JJA, SON) based on their standardized anomalies. An analysis of these cases is presented using time lag composites, and anomaly fields. Anomalies were calculated based on a 33-year weighted climatology. The analysis showed that the cases are characterized by air masses with distinct subtropical traits: reduced static stability, and anomalously high precipitable water. Persistent, slow moving upper- and lower-level features were essential in the build up of high-$\theta_e$ air in the Montreal region. The theta_e anomalies cover a large extent; thus, not only the Montreal area is impacted. A parcel trajectory analysis shows that parcel theta_e is not conserved, and that evaporative and radiative processes are important. The trajectory analysis also showed anticyclonic curvature to all paths in all seasons, implying that the subtropical anticyclone is important in the transport of high-theta_e air. An analysis of the thermodynamic equation shed light on the complexity of the rapidly changing thermal structures associated with the extreme air masses, further stressing the importance of non-adiabatic processes on these relatively short time scales. Finally, a case study study is presented, providing further insight on the synoptic-dynamic conditions leading to extremes in theta_e in Montreal, and their impacts.
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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 | 0.003 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".