Effects of Pressure on Collision, Coalescence, and Breakup of Raindrops. Part I: Experiments at 50 kPa
Bibliographic record
Abstract
Abstract Previous breakup experiments have been carried out at laboratory pressures (∼100 kPa). However, raindrop interactions mainly take place higher up in the atmosphere, even in the supercooled part of a cloud where drops can be initiated by shedding from hailstones. Thus, 50 kPa, corresponding to a height of ∼5.5 km in the atmosphere at a temperature of ∼−20°C, was selected to bracket the region of interest for rain. Six drop pairs were studied at 50 kPa and laboratory temperature (∼20°C), one of them with reduced surface tension. The apparatus consists of drop-producing nozzles, acceleration systems, deflectors, a timing and selection control, a pressure regulator, and a photographic unit, mostly set up in a low-pressure chamber. After acceleration to terminal speed, a smaller drop is blown into the path of the larger one while an electronic timing system selects suitable drop pairs that may collide, thereby triggering eight subsequent flashes with a frequency of up to 100 kHz. The results are displayed in terms of a normalized fragment probability per size bin, ready for parameterization in the Part II of this paper. Five drop pairs were studied in 772 individual events. Overall, 51% resulted in filament breakup, 22% in sheet breakup, 7% in disk breakup, and 20% ended in coalescence. No bag breakups were observed. When compared to the 100-kPa results, the fragment numbers increased at large collision kinetic energies (CKEs) by factors of between 2.64 and 4.37 with pressure decreasing from 100 to 50 kPa, and they remained unchanged at low CKE. Detailed diagrams and tables show the results for the different drop pairs and collision categories. Increasing the sensitivity of the optical measurements from 0.05 to 0.01 cm increased the number of recognized fragments by factors up to 4.4, but only for the two higher-CKE cases. The higher resolution did not increase the fragment numbers detected in the lower-CKE range.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".