Severe geomagnetic storm hits Northern Hemisphere with northern lights - San Francisco Chronicle

A large-scale geomagnetic storm hit the Northern Hemisphere Sunday night, but most Californians' hopes to spot colorful waves of light known as aurora borealis, or northern lights, were dashed by cloudy conditions on the West Coast that obscured the rare sightings from view. 

While the powerful geomagnetic storms caused by disruptions in Earth’s magnetic field create beautiful aurora, they can disrupt navigation systems and satellites and create harmful currents in the power grid and pipelines, according to the National Oceanic and Atmospheric Administration’s Space Weather Prediction Center. 

The agency predicted Sunday that the nighttime lights could be visible in Northern California, but later revised its predictions several times to say they would only reach as far south as Oregon or Washington. NOAA maps showed people in Oregon and Washington had a 20% to 50% chance of viewing aurora under clear weather conditions. 

Some observers held out hope, but the coast's famously cloudy skies did not cooperate. 

A layer of fog descended on the Bay Area and clouds shrouded much of the West Coast on Sunday evening, meteorologists said, meaning most  hoping to observe any celestial phenomena were out of luck. The approach of summer – with its longer stretches of daylight – didn't help either. 

“By the time it’s dark enough to see any aurora on the West Coast the aurora would have moved to higher latitudes,” said Vahé Peroomian, a professor of physics and astronomy at the University of Southern California. 

Meteorologists with the National Weather Service in Riverton, Wyo. -- a city at roughly the same latitude as Eugene, Ore. -- captured spectacular aurora with light waves in streaks of green, pink and purple against the night sky.

While California's chance of seeing aurora was slim, Peroomian said it was still worth keeping a lookout until 11 p.m. or so by which time the storm would have passed its peak.  

Geomagnetic storms occur when energy from the sun’s outermost atmosphere disrupts Earth’s magnetic field, causing bands of green and red to light up the night sky. The natural electrical phenomenon is especially visible near the North Pole, but sometimes stretches lower into Canada and the northern United States, where it is often captured by wildfire cameras. 

An aurora borealis brightens the northern horizon over Wolf Lake in the Cloquet State Forest in Minnesota in 2019. 

Alex Kormann/Getty Images 2019

NOAA trackers indicated that disturbances in the Earth’s magnetic field had more than doubled by Sunday evening. That influx of energy had the potential to cause power grid fluctuations and increased drag on low orbiting satellites. But NOAA scientists predicted the worst impacts would be felt overnight by people living at above 50 degrees latitude, which falls in northern Canada. 

“The sun releases large quantities of energy from its core in an explosive display that we call solar flares,” said Chronicle meteorologist Gerry Díaz, who added that the flareups propel charged particles toward Earth that are deflected by the planet’s magnetic field.

As the particles slam into Earth’s atmosphere, they produce flashes of colorful light. When vast numbers of particles hit the atmosphere, they can appear to move or “dance” in the night sky.

NOAA's Space Weather Prediction Center tracker uses a scale known as the planetary k-index that quantifies disturbances in the earth's magnetic field, with 1 being calm and 5 to 9 indicating a geomagnetic storm. The k-index value for much of Sunday afternoon and evening hovered between 7 and 8, indicating a storm big enough to push aurora to far lower latitudes than they usually reach. 

Reach Nora Mishanec: nora.mishanec@sfchronicle.com

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