Bz — The Aurora Intensity Dial — Aurora Guide
Bz — The Aurora Intensity Dial
The solar wind carries the Sun's own magnetic field to Earth. Scientists measure its north–south direction and call it Bz. It works like a dial that controls how strongly solar particles can pour into Earth's upper atmosphere.
Auroras can happen with Bz pointing in either direction — but the direction makes a huge difference to how bright and active they are.
↑ ↑ ↑
🌍
⚠️ Weak — faint aurora if Kp is high
Bz North (+)
Sun's field points the same way as Earth's
Fields resist each other — shield stays stronger
↓ ↓ ↓
🌍
✨ Strong — intense, dancing aurora
Bz South (−)
Sun's field points the opposite way to Earth's
Fields connect like opposite magnets — more particles flood in
The key insight: A positive Bz doesn't mean zero aurora — it means a weaker one. A negative Bz (southward) means the shield is more open and particles pour in more easily, making the aurora much brighter and more active. The more negative Bz is, the more intense the show.
Check tonight's aurora forecast