A powerful X-class solar flare on Jan. 18 launched a fast-moving coronal mass ejection (CME) that struck Earth on Jan. 19, triggering severe G4 geomagnetic storm conditions earlier than expected.

The shock wave arrived at 2:38 p.m. EST, and the storm remains ongoing, promising heightened aurora activity through the evening.

The impact of a CME depends on its magnetic orientation: a southward-directed field (Bz) can strongly interact with Earth’s magnetic field, while a northward field largely deflects it.

Many CMEs have mixed magnetic fields, causing fluctuating or stop-start geomagnetic activity, Space.com has reported.

Scientists will continue monitoring the CME’s effects in real time using spacecraft like DSCOVR and ACE to better understand its interaction with Earth’s magnetosphere.