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07-11-2024

Auroras are a visual warning of harmful shocks to Earth’s magnetic field

Auroras have inspired awe for millennia, but with modern reliance on electricity, we are only now understanding their full impact on Earth’s magnetic field.

The same forces behind auroras also produce currents that can harm electrical infrastructure, such as pipelines. 

Now, a study published in Frontiers in Astronomy and Space Sciences has shown that the impact angle of interplanetary shocks is crucial to the strength of these currents, offering a way to predict and protect against potential damage.

“Auroras and geomagnetically induced currents are caused by similar space weather drivers,” explained lead author Denny Oliveira, a scientist at NASA’s Goddard Space Flight Center.

“The aurora is a visual warning that indicates that electric currents in space can generate these geomagnetically induced currents on the ground.”

“The auroral region can greatly expand during severe geomagnetic storms. Usually, its southernmost boundary is around latitudes of 70 degrees, but during extreme events it can go down to 40 degrees or even further, which certainly occurred during the May 2024 storm – the most severe storm in the past two decades.”

Auroras and Earth’s magnetic field

Auroras occur through two primary processes: particles from the sun hitting Earth’s magnetic field, or interplanetary shocks compressing the magnetic field. 

These shocks also generate geomagnetically induced currents that can damage electrical infrastructure.

“The impact of interplanetary (IP) shocks on the Earth’s magnetosphere can greatly disturb the geomagnetic field and electric currents in the magnetosphere-ionosphere system,” wrote the study authors.

“At high latitudes, the current systems most affected by the shocks are the auroral electrojet currents.”

“These currents then generate ground geomagnetically induced currents that couple with and are highly detrimental to ground artificial conductors including power transmission lines, oil/gas pipelines, railways, and submarine cables.” 

Stronger shocks mean stronger currents and auroras, but frequent, less powerful shocks can also cause harm over time.

“Arguably, the most intense deleterious effects on power infrastructure occurred in March 1989 following a severe geomagnetic storm – the Hydro-Quebec system in Canada was shut down for nearly nine hours, leaving millions of people with no electricity,” said Oliveira. 

“But weaker, more frequent events such as interplanetary shocks can pose threats to ground conductors over time. Our work shows that considerable geoelectric currents occur quite frequently after shocks, and they deserve attention.”

Angle and timing of the shocks

Shocks hitting Earth head-on induce stronger geomagnetically induced currents due to greater compression of the magnetic field. The researchers studied how these currents vary with the angle of shocks and the time of day.

Using data from interplanetary shocks and geomagnetically induced currents recorded from a natural gas pipeline in Mäntsälä, Finland, they calculated the shocks’ properties, such as angle and speed, using interplanetary magnetic field and solar wind data.

Shocks were categorized into three types: highly inclined, moderately inclined, and nearly frontal.

The researchers found that more frontal shocks lead to higher peaks in geomagnetically induced currents, both immediately after the shock and during subsequent substorms. 

Intense peaks often occurred around magnetic midnight when the north pole was aligned between the sun and Mäntsälä, also causing striking auroral displays.

“Moderate currents occur shortly after the perturbation impact when Mäntsälä is around dusk local time, whereas more intense currents occur around midnight local time,” Oliveira explained.

Preventing damage to infrastructure

Predicting the angles of these shocks up to two hours in advance could enable preemptive measures to protect electrical grids and other infrastructure from the strongest shocks.

“One thing power infrastructure operators could do to safeguard their equipment is to manage a few specific electric circuits when a shock alert is issued,” Oliveira suggested. “This would prevent geomagnetically induced currents reducing the lifetime of the equipment.”

However, the study did not find a strong correlation between the shock angle and the time it takes to induce a current, likely due to the need for more data from different latitudes.

“Current data was collected only at a particular location, namely the Mäntsälä natural gas pipeline system,” said Oliveira. “Although Mäntsälä is at a critical location, it does not provide a worldwide picture.” 

“In addition, the Mäntsälä data is missing several days in the period investigated, which forced us to discard many events in our shock database. It would be nice to have worldwide power companies make their data accessible to scientists for studies.”

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