Millions Saw Unexpected Northern Lights

For two nights, dazzling auroras delighted sky-gazers in unexpected places, including in the US as far south as Florida. The cause: dual solar storms unleashed by the sun reaching Earth.

A severe storm was initially predicted for Thursday as well, with the potential for the northern tier of the US to see auroras again in the evening. Forecasters at the National Weather Service’s Space Weather Prediction Center now believe Wednesday night might have been the last opportunity for the most intense conditions.

In addition to creating auroral displays, geomagnetic storms can disrupt communications, the power grid and satellite operations. The Space Weather Prediction Center said it had otified power grid and satellite operators in the US so they could prepare.

The British Geological Survey initially believed the current solar activity could lead to a G5, or an extreme geomagnetic storm — the highest level on the scale. The survey also dubbed Tuesday’s event a “cannibal storm” that disrupted communications and GPS satellite accuracy.

“On Monday, two Coronal Mass Ejections lifted off the sun a few hours apart,” the survey’s geomagnetism team explained. “The first one was moving more slowly than the second … and so the second one caught up with the first one and they amalgamated together by the time they reached Earth. Hence, the term ‘cannibalised,’ as the second one gobbled up the first one.”

Coronal mass ejections, or CMEs, are large clouds of ionized gas called plasma and magnetic fields that erupt from the sun’s outer atmosphere. When these outbursts are directed at Earth, they can cause major disturbances of Earth’s magnetic field, resulting in geomagnetic storms.

Forecasters at the Space Weather Prediction Center believe that the arrivals of the first two of three anticipated coronal mass ejections caused Tuesday evening’s auroral display.

“One of them packed a much stronger punch than we would have imagined originally,” said Shawn Dahl, forecaster at the center.

When a storm reaches satellites stationed 1 million miles from Earth, forecasters can measure its speed, the strength of the magnetic field and the magnetic orientation, he said.

“Is it pointed opposite Earth, or is it pointed the same as Earth?” Dahl said. “If it turns opposite Earth, then activity really quickly escalates, and those storm levels can dramatically increase very quickly. That’s what happened last night.”

The third solar storm arrived at Earth Wednesday afternoon at 2:17 p.m. ET, with solar wind speeds over 2.1 million miles per hour (950 kilometers per second).

But Earth appears to have been struck by a far flanking edge of the storm, meaning most of the magnetic cloud likely missed our planet, according to an update from the center.

- Author: Ashley Strickland, CNN