On the formation of pre‐onset azimuthal pressure gradient in the near‐Earth plasma sheet
Bibliographic record
Abstract
Xing et al. (2011) demonstrated by case study that the plasma sheet pressure gradient at ∼11 REnear the substorm onset meridian undergoes a substantial duskward enhancement shortly before substorm onset as identified from the auroral poleward expansion. It was suggested that the increased upward FAC driven by this pressure gradient enhancement lead to the thin onset arc intensification from which the poleward expansion initiates. In the present study, we employ the multiTHEMIS spacecraft in azimuthal conjunction ‐at ∼−11 REand examine the ion flux and distributions during the period of pressure gradient enhancement, and identify two categories of events. For events with pressure gradient change ≤2 min prior to onset, strong earthward ion flux enhancements covering the energy range from several keV to above 25 keV were observed by the spacecraft identifying the higher pressure increase, while at the same time the ion distributions show a substantial earthward shift in velocity space. These resemble the ion acceleration ahead of earthward moving dipolarization fronts. On the other hand, the spacecraft observing the lower pressure increase found weaker or no ion flux enhancements and had nearly isotropic distributions, indicating that longitudinally localized dipolarization fronts are responsible for the pressure gradient development. These pressure gradient enhancements were in the duskward (dawnward) direction for measurements to the east (west) of the onset region. For pressure gradient enhancement >2 min prior to onset, stronger plasma sheet thinning was observed by the spacecraft identifying the larger pressure increase and the ion distributions appear nearly isotropic, which suggests plasma redistribution in the undisturbed plasma sheet. These two categories suggest that both dipolarization fronts and growth phase plasma sheet localized thinning can drive azimuthal pressure gradient enhancement near the onset meridian and cause pre‐onset thin auroral arc intensification, though the dipolarization front events appear to be substantially more common based on our 14 events.
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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 | 0.000 | 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) | 0.001 | 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".