Earth experienced a 12-hour minor geomagnetic storm followed by a three-hour strong geomagnetic storm between 9 am on September 29 and 2 pm on September 30. The global geomagnetic activity index (Kp) peaked at 7.33. Dazzling auroras lit up the sky in Jiamusi, northeast China's Heilongjiang Province, as a result of the storm, China Media Group (CMG) reported.

Notably, the storm occurred without any major solar flares beforehand, and with coronal holes that were not especially large. A high-speed stream of solar wind from a coronal hole was the likely driver. There is also the possibility of a so-called "stealth" coronal mass ejection (CME), or even a combination of both processes.

Another key factor is timing. The storm struck just days after the autumn equinox – a period when Earth is especially susceptible to solar magnetic influences. Because of the angle between Earth's equatorial plane and its orbital plane around the Sun, this angular difference reaches a minimum near the equinoxes, making Earth more vulnerable to geomagnetic disturbances.

With these conditions aligning, skywatchers around the world were once again treated to auroral displays.