Increasingly Parallel Pressure Anisotropic Ballooning: Substorm Growth Phase Drift Orbits Resulting in a Locally Ballooning Unstable Geomagnetic Tail
Bibliographic record
Abstract
Abstract Recent work by Oberhagemann and Mann (2020, https://doi.org/10.1029/2019GL085271 ) has shown that ballooning instabilities in the transition region between dipolar and taillike fields associated with substorm onset may be triggered by an anisotropic pressure distribution that moves from an initially mild perpendicular anisotropy toward more parallel anisotropy. Here we examine the mechanism which can result in this transition toward more parallel pressure during growth phase tail stretching. We trace particles through a two‐dimensional model magnetic field to examine the evolution of particle distributions as they periodically drift through a tail which changes from a less stretched, quiet time to a more stretched late growth phase configuration. Our findings show that these particle pitch angle distributions become more parallel anisotropic through a combination of drift shell splitting and preferential de‐energization in the perpendicular direction. Drift shell splitting causes low pitch angle particles from a high‐pressure region to mix with high pitch angle particles from a low‐pressure region in a radially localized area in the tail transition region where high earthward pressure gradients exist. Preferential de‐energization occurs due to a transfer of particles from less stretched to more stretched field lines that reverses the usual balance between Fermi and betatron acceleration and causes particle pitch angle distributions to become more field aligned. Our model predicts onset characteristics and location in good agreement with observations, with the most unstable region consistent with the location of the auroral beads, which accompany the onset of the expansion phase of many substorms.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.002 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".