An eruption of particles from the sun collided with Earth on Thursday morning.
The Space Weather Prediction Center, part of the National Oceanic and Atmospheric Administration, reported that the solar particles, which were ejected on Tuesday evening, arrived at 11:15 a.m. Eastern time, traveling at nearly 1.5 million miles per hour.
The center warned that the particles could generate strong geomagnetic storms on Earth that could damage satellites, mangle GPS signals and cause blackouts. They can also create brilliant auroras in night skies closer to the Equator than usual.
A watch issued on Wednesday that the solar storm could reach severe or extreme levels remains in effect.
This was the second such watch, which is the space weather equivalent of a hurricane watch, to be issued by the center in the past 19 years.
The first, in May, put the United States on alert for a severe solar storm that appeared to be on its way to Earth. That solar storm reached the highest level of “extreme,” but the early warning allowed electrical utilities to prepare and helped prevent major outages.
Periodically, the sun spews out explosions of particles known as coronal mass ejections.
When the solar eruptions are aimed right at Earth, the barrage of charged particles — protons, electrons and helium nuclei — can generate electrical currents and magnetic fields that may damage spacecraft and disrupt power grids.
Shawn Dahl, the service coordinator for the space weather center, said the storm would most likely not be as intense as the one in May. “The difference is, the one in May, we had a series of coronal mass ejections, one of them faster than the other,” Mr. Dahl said. “And it kind of swept everything together and just enhanced the effect.”
But the geomagnetic storm could last about 36 hours. If the storm reaches the severe level, the auroras in the Northern Hemisphere could stretch down into the middle of the United States, potentially as far south as Alabama.
The forecasts remained largely guesswork until the waves of particles reached two spacecraft, the NASA Advanced Composition Explorer, or ACE, and the Deep Space Climate Observatory, or DSCOVR, on Thursday.
Both are about one million miles from Earth, providing less than an hour of warning before the solar storm arrived our planet. At that point, the solar storm forecasters could analyze the structure of the coronal mass ejection and issue more specific warnings.
In May, the center started talking with power grid operators about six hours before the storm arrived.
This time, they reached out even earlier, because the power grid, already damaged by Hurricane Helene last month, will be further thrashed as Hurricane Milton bears down on Florida.
“With all the hurricane relief efforts going on and the inbound hurricane going into Florida and across the peninsula, we thought it prudent to immediately contact them now,” Mr. Dahl said. “We don’t know the true status there, but that’s just our concern.”
Neither the May eruption nor this week’s is as severe as the Carrington Event, a solar storm that hit Earth in 1859, disrupting telegraph stations, or another that in 1989 caused a nine-hour blackout in Quebec.
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