On the Origin of Far‐Aspect Angle Irregularity Regions Seen by HF Radars at 100‐km Altitude
Bibliographic record
Abstract
Abstract A special summer midday population of echoes has been reported by high‐frequency (HF) radars at ranges less than 300 km. These echoes come from a narrow altitude region near 100 km. Their spectral width indicates that they decay at a rate controlled by ambipolar diffusion. We label the echo regions as “far‐aspect angle irregularity regions” by contrast with “high‐aspect angle irregularity regions” (HAIR) documented in the past. Both types are from structures that decay after an initial growth phase. We show that each type decays at a rate controlled by the altitude where it is produced. The large aspect angles and decaying process come from a monotonic aspect angle increase due to a weak altitude dependence of the “eigenfrequency.” HAIR echoes are produced by the decay of otherwise standard E‐region irregularities. However, HAIR echoes are usually not far‐aspect angle irregularity regions because the latter are the result of a Gradient Drift Instability in the bottomside of the E‐region where the vertical density gradients can sometimes be so strong that a less than 10 mV/m northward electric field is able to destabilize 10‐m structures in the afternoon sector. Owing to smaller dip angles, the Gradient Drift Instability requirement is smaller at midlatitudes although it still needs a combined electron drift and eastward neutral wind contribution of the order of 100 m/s. With northward electric fields of 2 to 3 mV/m, the minimum midlatitude eastward wind requirement is of the order of 50 m/s.
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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 | 0.001 | 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".