May 23, 2024: (Spaceweather.com) Across the USA on May 10th and 11th, sky watchers marveled at bright displays of aurora borealis during the biggest geomagnetic storm in decades. Little did they know, something was also happening underfoot.

Strong electrical currents were surging through rocks and soil. The biggest voltages along the US eastern seaboard and in the Midwest were as much as 10,000 times normal. A map from NOAA and the US Geological Survey shows some of the ‘hot spots’ during the early hours of May 11th:

Back in March 1989, voltages only a little stronger than the ones shown above brought down the entire Hydro-Québec power system. The resulting Great Québec Blackout plunged millions of Canadians into darkness.

This time, however, power grids stayed up. “We haven’t heard of any serious problems so far,” reports Christopher Balch of NOAA’s Space Weather Prediction Center.

Balch leads an effort at NOAA to model geoelectric fields during solar storms. The map, above, is a snapshot from a real-time display that takes into account the 3D conductivity of the Earth and ongoing geomagnetic activity. A computer at the Space Weather Prediction Center crunches the data to produce minute-by-minute estimates of electricity in the ground.

When researchers talk about geoelectric fields they use units of volts per km (V/km). Earth’s crust naturally contains quiet-time fields measuring as little as 0.01 V/km. During geomagnetic storms, these values skyrocket.

“On May 10-11, geoelectric amplitudes exceeded 10 V/km in Virginia and 9 V/km in the upper Midwest,” says Jeffrey Love, a key member of the collaboration at the USGS. “These are very high. For comparison, we estimate that geoelectric amplitudes reached almost 22 V/km in Virginia during the March 1989 storm.”

This means the May 2024 storm was, electrically speaking, about half as intense as the storm that blacked out Québec 35 years ago. That’s too close for comfort. “Although power companies have taken measures to improve the resilience of their systems, no one would welcome another storm as intense as that of March 1989,” says Love.

Realtime electric field maps are published 24/7 on the NOAA website. During the next geomagnetic storm, click here to see what’s happening underfoot!