Solar Wind Density
Definition
How many particles the solar wind carries per unit volume, typically 1–10 per cubic centimeter.
In plain language
Density is how thick the wind is. A dense wind presses harder on Earth's magnetic bubble and delivers more particles — a sudden density spike often announces that a CME's compressed leading edge has arrived.
The science
Proton density at 1 AU varies from <1 to >50 cm⁻³. With speed it sets dynamic pressure (ρv²), which compresses the magnetopause; sheath regions ahead of CMEs commonly show sharp density enhancements.
Why it matters for aurora viewing
Watch for density spikes on telemetry: they frequently precede the magnetic-field swings that decide whether the night turns spectacular.
See this in action on tonight's data.