The northern lights may be visible across much of the U.S. tomorrow night thanks to a powerful cloud of solar plasma hitting our planet's magnetic field.
A "severe" G4 geomagnetic storm is forecast across October 10 and 11 as the plume of solar plasma—known as a coronal mass ejection, or CME—arrives at the Earth.
This geomagnetic storm could spark auroras in states as far from the north pole as California, as well as potentially causing voltage control problems in power grids and damaging spacecraft.
"The aurora may become visible over much of the northern half of the country, and maybe as far south as Alabama to northern California," NOAA's Space Weather Prediction Center said in a Geomagnetic Storm Watch.
Coronal mass ejections are flung out from the active areas of the sun's surface like sunspots, and often accompany a solar flare. This oncoming CME was released from sunspot AR3848 at the same time as a powerful X1.8-flare on October 8.
CMEs travel at several million miles an hour—compared to the light-speed rate of solar flares—and can generate geomagnetic storms in our atmosphere when they interact with Earth's magnetic field. The collision compresses and distorts the magnetosphere, and if the alignments of our magnetic field and the magnetic field of the CME are just right, it can result in the charged particles from the CME being channeled down into our atmosphere.
This can result in the aurora being seen further away from the north and south poles than normal. As the magnetic field lines are stretched and reconnected during a geomagnetic storm, the charged particles are funneled into the atmosphere at lower latitudes than usual, extending the northern lights to regions that are normally too far south to see it.
Different gases emit different colors of light when excited by these solar particles, with oxygen creating green light at lower altitudes and red light at higher altitudes, and nitrogen creating purple-blue light. This is why the northern lights appear more red the further south you go, as observers can only see the highest-altitude light.
Geomagnetic storms can also result in a variety of issues with infrastructure around the world, and in space.
"If a CME does impact the Earth, it can cause problems in communications and navigation systems and indeed cause problems with electrical power grids," Peter Gallagher, head of astronomy and astrophysics and director of the Dunsink Observatory at the Dublin Institute for Advanced Studies, told Newsweek. "For example, the Swedish air traffic control system was interrupted for several hours in 2015 causing the grounding of airplanes in Swedish airspace, while power grids in the U.S. and Canada were interrupted in 1989."
Geomagnetic storms have different impacts depending on how strong they are, and they are ranked on a scale of G1 (minor) to G5 (extreme). There are about 1,700 G1 storms per 11-year solar cycle, while there are only usually around 100 G4 and 4 G5 storms in this same period. The G5 storm that occurred on May 10 this year resulted in the northern lights being visible across all 50 U.S. states.
The SWPC predicts that the upcoming G4 geomagnetic storm could cause "possible widespread voltage control problems and some protective systems may mistakenly trip out key assets from the power grid, and that "systems may experience surface charging; increased drag on low earth orbit satellites, and tracking and orientation problems may occur."
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