June 13, 2022: Researchers have mapped the best and worst places to be in the USA during a severe geomagnetic storm. For residents of some big cities, the news is not good.
„Resistive structures in the crust and mantle of the Earth make cities along the east coast of the USA especially vulnerable to geomagnetic storms, “says Jeffrey Love of the US Geological Survey (USGS), who led the study. „The hazards are greatest for power systems serving Boston, New York, Philadelphia, Baltimore, and Washington, DC, – a megalopolis of over 50 million people. “
These conclusions are based on a new study of the biggest geomagnetic storm of the Space Age–the Great Québec Blackout. On March 13, 1989, two major CMEs hammered Earth’s magnetic field, knocking out the Hydro-Québec power grid. Millions of Quebecois spent a long winter night without heat or light.
What would happen if the same geomagnetic storm struck again? That’s what Love’s team wanted to find out. Back in 1989 while the lights were out in Québec, magnetic observatories around North America recorded the details of the storm. Love’s team combined those old data with new measurements of deep rock to map modern hazard zones.
Freshman physics students know that changing magnetic fields cause electrical currents to flow through conductors. It’s called „Faraday’s Law,“ and it happens during every geomagnetic storm. Earth’s magnetic field shifts and vibrates, inducing currents in everything from the rocks and dirt beneath your feet to the power lines running overhead. Earth itself forms an electrical circuit with power lines, and if too much current flows into the power grid it can cause a blackout.
In 1989 researchers didn’t have much detailed information about the Earth-half of the circuit. That has changed. In 2006, the National Science Foundation-funded Earthscope project began sounding our planet’s crust around North America to determine the 3D electrical properties of deep rock; the project is now being continued with funding from the USGS. It turns out, there are huge variations in conductivity from place to place. The type of rock a city sits on determines how vulnerable it is to geomagnetic storms.
In retrospect, Québec is especially vulnerable. The province sits on an expanse of Precambrian igneous rock that does a poor job conducting electricity. When the March 13th CME arrived, storm currents found a more attractive path in the high-voltage transmission lines of Hydro-Québec. Unusual frequencies (harmonics) began to flow through the lines, transformers overheated and circuit breakers tripped.
Assuming that the Québec storm was underway again, Love’s team mapped electric fields around much of North America. Measured in units of Volts per kilometer (V/km), these fields predict how much current will be pushed through wires at ground level. The higher the value, the bigger the hazard.
„Peak 1-min-resolution geoelectric field amplitudes ranged from 21.66 V/km in Maine and 19.02 V/km in Virginia to <0.02 V/km in Idaho,“ says Love. „Our maps show where utility companies might concentrate their efforts to mitigate the impacts of future magnetic superstorms.“
With Solar Cycle 25 ramping up to a new Solar Maximum expected in 2025, the new maps are coming not a moment too soon.
You can read Love et al.’s original research in the May 2022 edition of the research journal Space Weather. Click here.
June 12, 2022