20 Years Ago, A Severe Geomagnetic Storm

Oct. 21, 2021: Paolo Bardelli will never forget Oct. 21, 2001. “The sky over my hometown in Italy suddenly filled with intense red auroras,” he recalls. “This happened exactly 20 years ago today.”

Above: Red auroras over Tradate, Italy (latitude +45N), on Oct. 21, 2001. Photo credit: Cesare Guaita

A trip down memory lane: In 2001, Solar Cycle 23 was peaking and solar activity was very high. Strong flares were a daily occurance. On Oct. 19th, giant sunspot AR9661 erupted twice in quick succession, producing almost identical X1.6-class solar flares. The double blast hurled two bright CMEs toward Earth: CME #1, CME #2.

This is what the sun looked like that day:

The first CME took only two days to reach Earth. It was fast and potent. The storm cloud’s arrival on Oct. 21, 2001, 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.

In Troutman, North Carolina, Ronnie Sherril witnessed the CME’s impact. “Auroras were visible in twilight even before the evening sky faded to black,” says Sherril, who took this picture at 7:30 pm local time:

“By 10:30 pm the sky had exploded into bright red with yellowish beams,” says Sherril. “What an awesome display!”

Less than a day later the second CME arrived, and it happened all over again. Another 15 hours of strong-to-severe storming ensued. Using data from a global network of magnetometers, NOAA made this record of planetary K-indices during the two-day event:

Red auroras were sighted in Germany, France, Italy, Spain, Australia, Japan, and in the United States as far south as latitude 35N. Remarkably, there were no widespread power outages or satellite disruptions. The Internet functioned normally throughout. It was mainly an aurora show.

Some observers are ready for more. “We are hoping for something similar for Solar Cycle 25, as the sun has recently had a good increase in its activity,” says Bardelli. Indeed, young Solar Cycle 25 is intensifying, but Solar Max isn’t expected for another 3 to 4 years. Until then, browse the October 2001 Aurora Photo Gallery.

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