Confirmation of quasi‐perpendicular shock reformation in two‐dimensional hybrid simulations
Bibliographic record
Abstract
Shock reformation involves regions of a shock undergoing periodic collapse and redevelopment on a time scale close to the ion cyclotron period. Reformation is often observed in one‐dimensional (1‐D) hybrid and particle in cell (PIC) simulations of quasi‐perpendicular collisionless shocks provided the Alfvén Mach number MA and ion plasma beta βi are sufficiently high and low, respectively. Initial 2‐D PIC simulations showed some evidence for shock reformation, with ion reflection providing the main energy dissipation mechanism, while recent spacecraft observations showed a reforming shock with large amplitude whistler waves in the foot region. While recent spacecraft observations showed an case with reforming shock crossing with whistler waves dominated in the foot region. However, recent 2‐D hybrid and PIC simulations suggest that reformation does not occur in exactly perpendicular 2‐D shocks. This paper re‐examines shock reformation in quasi‐perpendicular shocks using 1‐D and 2‐D hybrid simulations. We find that 2‐D quasi‐perpendicular shocks (θbn = 85°) indeed undergo cyclic reformation providing MA and βi are high and low enough, respectively. For low MA ≤ 4, 2‐D quasi‐perpendicular shocks are found to be quasi‐stationary, despite 1‐D simulations predicting reformation, confirming and extending recent work for perpendicular 2‐D shocks. The dynamics of reformation are quite different in 2‐D than in 1‐D: in 2‐D large amplitude whistler waves grow in the shock foot, have amplitudes of order the downstream magnetic field, and affect the reformation. The whistlers have almost zero phase speeds in the shock frame and oblique wave vectors with respect to the upstream magnetic field. The predicted reformation period increases in 2‐D compared with 1‐D and increases nonlinearly as MA decreases towards the reformation threshold.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".