What is 'induced atmospheric vibration' and did it really cause power outages across Spain and Portugal?

In a rare international blackout, all of Spain and Portugal, as well as parts of southwest France, lost power on Monday morning (April 28).

The power cut caused massive disruptions across the region, with airports coming to a standstill, people becoming stranded on metro trains in Lisbon and Madrid, and hospitals being forced to cancel operations.

The exact cause of this blackout remains unclear, though representatives of Portugal's electricity network provider Redes Energéticas Nacionais (REN) said on Monday that it occurred due to a rare phenomenon called "induced atmospheric vibration."

"Due to extreme temperature variations in the interior of Spain, there were anomalous oscillations in the very high voltage lines (400 kV), a phenomenon known as 'induced atmospheric vibration,'" REN told the Guardian. "These oscillations caused synchronisation failures between the electrical systems, leading to successive disturbances across the interconnected European network."

However, REN has since refuted this explanation, Euronews reports.

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"The blackout that hit the entire territory of mainland Portugal today is the result of a significant voltage fluctuation in the Spanish grid at a time when Portugal was importing energy from Spain," REN said in a statement on Monday afternoon. "With this fluctuation, the control and protection systems of the Portuguese power plants, as expected in a situation with this configuration, shut down, causing the blackout."

Extreme temperature variations can cause strange oscillations in very high voltage power lines, physically moving back and forth. This is due to temperature changes causing the lines to expand in some places, changing tension in the lines, altering their aerodynamic properties, and interacting with wind and electrical current, which can physically and electrically destabilize the power system.

"Although investigations are ongoing, some early media reports are mentioning a phenomenon known as '"induced atmospheric vibration'" linked to unusual atmospheric conditions, including rapid temperature variations and resulting wind patterns in the interior of Spain," Victor Becerra, a professor of power systems engineering at the University of Portsmouth in the U.K., said in a statement.

"If these conditions have been in place they may have triggered abnormal oscillations in very high-voltage power lines," Becerra said.

This can snap conductors, short circuits or damage infrastructure like transmission towers.

"Protection systems are designed to automatically disconnect affected power lines in response to such faults," Becerra said.

Then, a kind of domino effect occurs, with the shutoffs causing instability and disconnection in some generators. "The loss of large generators can create a sudden and significant imbalance between power supply and demand in the power grid, potentially escalating into widespread outages," Becerra said.

The exact cause of the blackouts has not been confirmed, however, and some others have suggested that it could have been the result of a cyber attack. There is no evidence to suggest that this is the case, Senior European Commission vice-president Teresa Ribera told Spain's Radio 5 on Monday. On Tuesday (April 29), Eduardo Prieto, the head of services for Spanish grid operator Red Eléctrica's told the Guardian that they had ruled out a cybersecurity incident.

Regardless of the initial cause, such a large region was affected because European power grids are highly interconnected. Usually, that allows for greater reliability, with other grids providing backup if a local issue arises. But it also leaves the entire system vulnerable to large failures propagating across a much greater area.

"Electrical grids are large interconnected systems, and their stability is related to a very close balance between electricity generation and demand," Grazia Todeschini, an engineering researcher at King's College London, said in a statement. "If one area is disconnected, it can cause knock-on effects in nearby areas that may rely on supply (or demand) from the affected area."

Todeschini added that while some measures do exist to limit the impact of outages in small areas, they can be easily overwhelmed if the power imbalance is too large, causing outages to spread very quickly and very far.

Power losses of this scale have happened before. A 12-hour blackout across much of Italy in 2003 was triggered by an issue with a hydroelectric power line between Italy and Switzerland, and a 2006 temperature-driven power surge in Germany caused power cuts across France, Italy, Spain, Belgium and even Morocco. One of the largest blackouts in history occurred in India in 2012, affecting over 600 million people.

As of Tuesday morning, power is slowly returning to much of the Iberian Peninsula. All of Portugal and 99% of Spain now have electricity, and authorities are working to figure out the true cause of the incident, and stop it from happening again.