What the model provides
NOAA's OVATION product represents auroral activity around both magnetic poles on a global grid. The operational data include an observation time, forecast time and values by latitude and longitude. The lead is commonly around thirty minutes but varies with solar-wind travel time.
The output is not a photograph and does not show clouds, daylight or local obstructions. It is a model driven by upstream conditions and should be labelled with the valid time rather than described as an unqualified live camera.
Why the forecast lead is short
Spacecraft upstream of Earth sample the solar wind before it reaches the magnetosphere. The distance and measured speed provide a limited warning window. Faster flow shortens that travel time; data gaps or propagation uncertainty reduce confidence.
This near-Earth measurement captures the magnetic orientation that longer-range solar observations cannot determine precisely. Better knowledge arrives closer to impact, which is why detailed nowcasts and multi-day outlooks have different jobs.
How GreenHalos transforms the grid
GreenHalos validates timestamps, coordinate ranges and grid completeness, then converts the large source JSON into a compact versioned binary texture. The source payload hash and source identifier remain attached to the derived object, and a manifest points to immutable files.
The browser retrieves only first-party static data. It does not call NOAA during an ordinary pageview. A shader maps model values to a restrained activity visualisation; its green, cyan, purple and red colours are design encodings, not measured optical emission wavelengths.
Freshness changes the claim
GreenHalos labels OVATION live only while it falls within the configured live threshold. The states then move through recent and stale before invalid. A stale texture can remain visible only with its true timestamp and a clear warning; the interface must stop pulsing a live indicator.
An invalid or unavailable source cannot be replaced by an empty object or silently advanced clock. Static explanatory content and an official NOAA link remain available when the model cannot be shown.
What OVATION cannot promise
The model does not guarantee that aurora will be visible to a person at a coloured coordinate. Darkness, cloud, light pollution, terrain, viewing direction, individual eyesight and short-lived structure all matter.
OVATION also must not be stretched into a precise day-four-to-ten local forecast. GreenHalos uses Kp and broad geomagnetic outlooks at those horizons and explicitly avoids a fictitious future oval.
Evidence register
Primary sources
Sources were checked on . Each record identifies which sections it supports.
- Aurora - 30 Minute Forecast NOAA Space Weather Prediction Center Supports: What the model provides; Why the forecast lead is short; What OVATION cannot promise
- Latest OVATION aurora data NOAA Space Weather Prediction Center Supports: What the model provides; How GreenHalos transforms the grid