cams-aerosol-anomaly

○unverified

Parameterized ALERT LAYER (docs/spec/ALERTS.md §2.2, §10.2 pilot): fire where the current CAMS AOD550 near-real-time value exceeds its own recent history by more than N sigma over a user-chosen baseline window. The threshold is the USER's, not the operator's — this is the gap the incumbent CAMS Aerosol Alerts service leaves open (it bakes fixed high / very-high / extreme tiers against a 2003–2018 climatology; here `sigma` and `baseline_window` are subscription parameters). The recipe is a TEMPLATE, not a concrete layer. `params: { sigma, baseline_window }` are supplied per-subscription via `layer_params` (ALERTS §2.2), so one σ=2 subscriber and one σ=3 subscriber share the same layer definition without materializing `cams-aod-sigma-2` / `cams-aod-sigma-3` variants. Because the op's z-score is sigma-independent, a stricter σ always yields a SUBSET of a looser σ's firings over the same inputs. Method: 1. Ingest CAMS Global Atmospheric Composition Forecast AOD550 (NRT), windowed to the AOI, gridded onto the alert cell system (H3 r6). 2. Slice `baseline_window` into a per-cell baseline series (the "normal" reference); the newest observation is the `current` value being scored. The event under test is held OUT of the baseline. 3. anomaly_score (folia-engine op): per cell compute μ, σ_baseline, and z = (current − μ) / σ_baseline; fire where current >= μ + sigma·σ_baseline. 4. Emit a cell-indexed alert layer whose `flag`/`z_score` is thresholdable by the subscription (ALERTS §2 alert-layer convention). Separation of concerns (ALERTS §2.2): - Layer math : anomaly_score with the declared parameters - Layer instance : one subscriber's σ=3, another's σ=2 (via layer_params) - Subscription taste: when to actually notify ME (§3 trigger.threshold on the emitted flag/z_score) — NOT the same knob as sigma.