# RMO91 — why use a near-perpendicular model for 13 June 2010?

**Result in one sentence:** published magnetic modelling makes a near-perpendicular shock nose plausible, while an exact 90° angle and stationary upstream plasma remain assumptions of the checked RMO model.

This continues the RMO89 source-dependency assessment. It adds evidence provenance; it does not change any numerical result or claim an independently identified solar MHD type.

## What the existing publications actually contribute

| Question | Available support | How RMO should use it |
| --- | --- | --- |
| Are the EUV and radio signatures related? | Ma associates their onset with the same eruption. | Event-level support; not a resolved radio/EUV patch match. |
| Where does the radio emission originate? | Heights are inferred through density models. | Keep model-dependent heights distinct from radio imaging. |
| Why investigate near-perpendicular geometry? | Kozarev's PFSS overlay motivates a possible quasi-perpendicular nose. | Qualitative magnetic-model support; no numerical angle bound. |
| Why is B_n exactly zero in the calculation? | Ma's thermal reconstruction adopts perpendicular jump equations. | A specified limiting model, not a measured angle. |
| Is the upstream plasma at rest? | No matched upstream normal flow is supplied in the reviewed records. | Retain zero flow as an assumption and preserve the RMO88 sensitivity result. |
| Do the thermal and kinematic inputs describe identical volumes? | Regional DEM and selected EUV traces have different spatial definitions. | Keep this association dependency in the observation model. |

Sources: [Ma et al. (2011), Sections II and III.1–III.3](https://arxiv.org/html/1106.6056v1); [Kozarev et al. (2011), Sections III.1, III.2, III.4 and Figure 4](https://arxiv.org/html/1406.2372v1). The structured record in `observer_evidence/sources.json` gives the individual locators and evidence status.

## The positive conclusion

The perpendicular reconstruction has a physical motivation in the literature. It is useful to explore whether a shock of this kind can reproduce the supplied constraints and whether its diagnosis survives errors. RMO89 already established conditional consistency across its adopted scalar bounds.

The new source reading adds the reason for choosing that model. It does not supply a second numerical angle measurement. A closed field configuration by itself is insufficient to calculate the angle: the magnetic vector and the local front normal must be paired at one position and time. A model-derived angle could still be useful, provided its origin and uncertainty are retained.

## Three levels of association

1. **Same eruption:** supported by the published timing and context.
2. **Same shock surface or nose:** an interpretation supported by the authors' comparisons and models.
3. **Same local patch at the diagnostic time:** not recovered as a direct radio-image/field/normal match in the reviewed material.

These levels should not be collapsed into a single yes/no flag. Event-level association is scientifically useful; a local jump inversion asks a more spatially specific question.

The radio height consistency and its density-derived speed also share a model dependency. They should not be counted as two independent position and velocity measurements. Likewise, magnetic strength or downstream temperature reconstructed from shock equations is an output of that interpretation.

## Consequence for the next calculation

The current B_n=0 result applies to its exact geometry. Qualitative support for a nearly perpendicular nose does not automatically extend that result to finite nonzero B_n. A future departure-from-perpendicular study would have to construct conservation-linked states, check all relevant characteristic and admissibility conditions, and clearly label any chosen angle range as a model scenario unless observational bounds become available.

Similarly, a model normal speed and an upstream plasma speed must be distinguished. The incoming speed in the front frame depends on their difference along the same normal. The previously checked upstream-flow sensitivity remains relevant; the present literature reading supplies no new numerical bound on that flow.

A useful next observational input would therefore be a local angle estimate from a matched front surface and magnetic model, with its uncertainty and provenance. This would constrain a scenario rather than silently replace unknown geometry by exactly 90°. Direct or explicitly model-based upstream-flow information and the matched emission comparison remain additional dependencies. This checkpoint starts no new data acquisition or numerical campaign.

## What changed in QuickLook?

The solar example now contains **Why this solar geometry?**, opening a compact evidence table and this explanation. Existing results, figures, model inputs, scripts and reports remain available. No unknown input is filled and no classification label is assigned by the new section.

Static preservation and navigation checks are recorded in `results/observer_evidence/verification.json`. They do not validate native Chrome rendering or downloads. No new physical solver execution was needed for this source audit.