A Coronal Mass Ejection (CME) is a massive eruption of magnetised plasma from the Sun. When it hits Earth's magnetosphere, it can trigger geomagnetic storms, radiation hazards, and — most visibly — the aurora. Here's how the entire chain works.
A Coronal Mass Ejection (CME) is a massive eruption of magnetised plasma from the Sun. When it hits Earth's magnetosphere, it can trigger geomagnetic storms, radiation hazards, and — most visibly — the aurora. Here's how the entire chain works.
CMEs originate from the Sun's corona, often associated with solar flares. A billion tonnes of plasma launches into space at 250–3,000 km/s.
When a CME reaches Earth, its compressed magnetic field slams into the magnetosphere. If the CME's magnetic field has a strong southward Bz component, the shield cracks open.
The explosive reconnection in the magnetotail accelerates charged particles along magnetic field lines towards the poles. When they hit the upper atmosphere, they excite atoms — producing light.
DSCOVR at L1 gives ~15–45 minutes warning of CME arrival. After impact, the magnetosphere takes 30–60 minutes to fully energise. The aurora can then persist for hours, with substorm intensifications every 1–3 hours.
The aurora is the visible end of a chain reaction that starts 150 million kilometres away. Understanding the chain helps you predict when — and where — to look up.