Auroral wave structures and ballooning instabilities in the plasma sheet
Bibliographic record
Abstract
Abstract Auroral wavelike structures extended in the east‐west direction along preexisting arcs are often observed to precede the auroral poleward expansions initiated along that arc. These wave structures are suggested to be the manifestation of ballooning/interchange instabilities in the near‐Earth plasma sheet that may play crucial roles in leading to substorm expansion. The triggering and the development of the ballooning instability in the MHD regime can be evaluated with theory and numerical simulations; however, observations have never shown how these instabilities are initiated in the plasma sheet. In order to examine the instability triggering, we take advantage of the THEMIS ground all‐sky‐imagers and NORSTAR‐NASCAM multiwavelength imagers together with a multi‐spacecraft conjunction to identify the auroral wave structures and to examine the dynamics in the plasma sheet. We show in a case study that the MHD ballooning instability criterion is violated near X = −11 RE in the plasma sheet starting about 1.5 min prior to the initiation of the auroral wave structures. The estimated Alfvénic transit time is slightly larger than 1 min, indicating that the observed auroral signatures are correlated with the ballooning instability developing in the plasma sheet and propagating to the ionosphere along field lines. Magnetic field wavelet analysis shows the initiation of the perpendicular disturbances between 0.01 and 0.02 Hz correlated with the calculated onset of the instability perturbations at the same location, supporting the identification of the localized ballooning instability. At the more tailward region of X ~ −13 RE, enhanced earthward transport toward the unstable region are observed several minutes prior to the instability initiation, which may have modified the pressure spatial distribution and magnetic field topology in the near‐Earth region, leading to the violation of the instability criterion. The further development of the instability may play a crucial role for the aurora explosive expansion.
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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) | 0.000 | 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 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".