G1 MODERATE Geomagnetic Storm — 2026-10-04

A geomagnetic storm is a temporary disturbance of Earth's magnetosphere caused by solar wind activity. These storms are triggered by coronal mass ejections (CMEs) or high-speed solar wind streams that compress and distort Earth's magnetic field. The most visible effect is the aurora borealis (northern lights) and aurora australis (southern lights), which can extend to much lower latitudes during major storms.

When a CME or solar wind stream reaches Earth, it carries a magnetic field. If this field is oriented southward (opposite to Earth's), it connects with Earth's magnetosphere through a process called magnetic reconnection. This injects energy into the magnetosphere, accelerating charged particles along magnetic field lines toward the polar regions. When these particles collide with oxygen and nitrogen in the upper atmosphere, they emit photons — creating the aurora.

Geomagnetic storms follow the approximately 11-year solar cycle. During solar maximum, storms are more frequent and more intense. Even during solar minimum, recurrent high-speed wind streams from coronal holes can produce moderate storms on a 27-day rotation cycle. The Kp index measures geomagnetic activity on a scale of 0-9, with G1 (minor) storms starting at Kp 5 and G5 (extreme) storms at Kp 9.