On quasigeostrophic dynamics near the tropopause
Bibliographic record
Abstract
Under quasigeostrophic (QG) dynamics, the presence of a sharp transition in the stratification profile leads to the formation of comparably sharp vertical gradients of buoyancy. When the QG potential vorticity is assumed to be confined to the jump region, as in surface quasigeostrophy (SQG), the sharp gradients are present initially in the buoyancy field. If smoothly varying initial conditions are considered instead, jump-scale features nevertheless emerge after a few turnover times. Inspection of the omega equation reveals that vertical velocity is vertically smoother than buoyancy. As such, the vertical velocity cannot compensate for the sharpness of the stratification jump in the buoyancy equation. Consequently, buoyancy evolves differently above and below the model tropopause, quickly generating sharp vertical gradients. This is confirmed by numerical simulations. The introduction of this small scale, h, characterizing the tropopause implies a larger Froude number, thereby undermining the validity of the quasigeostrophic approximation. For fixed h, scale analysis gives a characteristic horizontal velocity, U, above which not only does QG break down, but statically unstable conditions also develop. Using typical atmospheric values for the Brunt-Väisälä frequency, N = 0.01 s−1, and the jump width, h = 100 m, we argue that U must be less than about 1 ms−1 for static stability to hold (and smaller still for quasigeostrophy to be formally valid). Therefore, quasigeostrophic dynamics are consistent only with very weak near-tropopause flows and thus can hardly account for the observed wind profiles (e.g., the Nastrom and Gage spectral break). We also find that initially smooth flows exhibit secondary roll-up of filaments and shallow slopes near the model tropopause, reminiscent of SQG dynamics. These flows, however, are not SQG-like in the sense they have non-vanishing vertical velocities at the tropopause.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".