An aurora witnessed in Hokkaido on March 18 this year, the first one there in 11 years, was caused by two successive magnetic storms near the Earth, according to a team of researchers.
Auroras occur when high energy particles from the sun light up the Earth's atmosphere. Normally they are observed near the North or South Pole, at high latitudes, and are rarely seen in places like Hokkaido. Low-latitude auroras have been attributed mainly to large explosions on the surface of the sun, but in the March case, there was not an especially large amount of activity on the sun.
The researchers analyzed data including electric currents around the Earth at the time of the aurora, and also looked into how magnetic storms form from disrupted magnetism around the Earth. They concluded that on March 17 a small magnetic storm occurred, and before the recovery from this a second, medium-scale magnetic storm occurred, which then developed into a large-scale magnetic storm.
Magnetic storms can interfere with communications and satellites, and Yosuke Kamide, professor emeritus at Nagoya University and one of the researchers, says, "This magnetic storm was the largest in recent memory. We need to look not only at the sun but closer to the Earth and predict magnetic storms."
The research results were published in an academic journal of the American Geophysical Union.