In 2001, Solar Cycle 23 was peaking and solar activity was very high. On Oct. 19th of that year, giant sunspot AR9661 erupted twice in quick succession, producing almost identical X1.6-class solar flares. The double blast hurled two CMEs toward Earth.
The first CME arrived on Oct. 21st. Its impact jolted Earth’s magnetic field and ignited a severe geomagnetic storm (Kp=8). Solar wind speeds in the CME’s wake topped 700 km/s, keeping the storm going for more than 15 hours.
On Oct. 22nd, the second CME arrived, and it happened all over again! Red auroras were sighted in Germany, France, Italy, Spain, Australia, Japan, and in the United States as far south as the Carolinas. [SOURCE]
