March 31, 2021: What a difference 20 years makes. Today the sun is blank and featureless as Solar Cycle 25 struggles pull solar activity from the doldrums of a deep Solar Minimum. In March 2001, however, the solar disk was peppered with sunspots, including a monster named „AR9393.“ The biggest sunspot of Solar Cycle 23, AR9393 was a truly impressive sight, visible to the naked eye at sunset and crackling with X-class solar flares.

On March 29, 2001, AR9393 hurled a pair of CMEs directly toward Earth. The first one struck during the early hours of March 31, 2001. The leading edge of the shock front was dense (~150 protons/cc) and strongly magnetized — traits that give rise to powerful geomagnetic disturbances. Within hours, an extreme geomagnetic storm was underway, registering the maximum value of G5 on NOAA storm scales.

„I was fortunate to witness and photograph the event when I was just a teenager,“ recalls Lukasz Gornisiewicz, who watched the show from Medicine Hat, Alberta:

In the hours that followed, Northern Lights spread as far south as Mexico. In 20 year old notes, Dr. Tony Phillips of describes „red and green auroras dancing for hours“ over the Sierra Nevada mountains of California at latitude +37 degrees. Similar displays were seen in Houston, Texas; Denver Colorado; and San Diego, California.

„Here in Payson, Arizona, red curtains and green streamers were pulsating all across the sky,“ wrote Dawn Schur when she submitted this picture to 20 years ago:

„We have seen some auroras here before, but this display was really special,“ she wrote.

A second CME struck at ~2200 UT on March 31th. Instead of firing up the storm, however, the impact quenched it. When the CME passed Earth the interplanetary magnetic field surrounding our planet suddenly turned north — an unfavorable direction for geomagnetic activity.

Indeed, the quenching action of the second CME may have saved power grids and other technological systems from damage. The storm’s intensity (-Dst=367 nT) stopped just short of the famous March 14, 1989, event that caused the Quebec Blackout (-Dst=565 nT) and it was only a fraction of the powerful Carrington Event of 1859 (-Dst=~900 nT).

The whole episode lasted barely 24 hours, brief but intense. Visit archives for March 3031st and April 1, 2001, to re-live the event. Our photo gallery from 20 years ago is a must-see; almost all the pictures were taken on film!

March 30-31, 2001, Aurora Photo Gallery
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via Spaceweather