The biggest disturbance of Earth’s magnetic field in more than 20 years dazzled onlookers the world over
By MICHAEL GRESHKO, Science.
Excerpt: Earth got its bell rung this past weekend, sucker-punched by the Sun itself in the biggest geomagnetic storm in more than 2 decades. The storm—triggered when the magnetic fields in blobs of plasma from the Sun collided with Earth’s magnetic field—not only yielded once-in-a-generation aurorae at latitudes as low as the Florida Keys, but also took scientists’ breath away with its power. ...This weekend’s fireworks began with Active Region 3664, a giant cluster of sunspots, more than 15 times wider than Earth, where the Sun’s magnetic field is highly concentrated. The magnetic field lines twisted and eventually snapped, causing the cluster to fling off a series of enormous, billion-ton blobs of plasma toward Earth, each embedded with strong magnetic fields. The detection of at least five of these expulsions, known as coronal mass ejections (CMEs), caused U.S. forecasters to issue a “severe” G4 watch—its first since 2005—on 9 May, the day before the blobs struck Earth. ...as they moved toward Earth, they coalesced into a single complex mass. ...The storm was upgraded to an extreme G5. ...Geomagnetic storms that approach this weekend’s severity occur about four times per 11-year solar cycle, according to the Space Weather Prediction Center (SWPC) of the National Oceanic and Atmospheric Administration. The last G5 resembling this weekend’s event, the so-called “Halloween storms” of 2003, caused power outages in Sweden and blew out transformers in South Africa. Another G5 storm in 1989 knocked out power for 6 million people in Quebec in Canada.....