Imma Perfetto
Cosmos science journalist
When the Hunga Tonga-Hunga Ha‘apai volcano erupted on 15 January 2022, it devastated the Kingdom of Tonga and sent literal and metaphorical shockwaves around the world.
It had been nearly 140 years since an eruption of this size shook the Earth, but scientists are only now beginning to document just how big it really was.
The extent to which it affected the planet, and even influenced weather patterns in space, has been reported in two different studies published this week.
The first study, published in the journal Science, has found that atmospheric waves produced from the massive eruption circled the entire globe four times in one direction, and three times in the other.
Scientists have also discovered that winds produced by these waves even reached the ionosphere and influenced weather patterns in space, according to a second study published in Geophysical Research Letters.
Atmospheric waves circled the globe
An international team of geophysicists published the Science study – first comprehensive account of the eruption’s atmospheric waves. They claim they’re the strongest recorded from a volcano since the 1883 Krakatoa eruption in Indonesia.
“This atmospheric waves event was unprecedented in the modern geophysical record,” says lead author Robin Matoza, an associate professor at the University of California Santa Barbara’s Department of Earth Science in the US.
The event has provided unique insight into the behaviour of a variety of atmospheric wave types which, according to co-author Dr David Fee from the University of Alaska Fairbanks Geophysical Institute, US, “has implications for monitoring nuclear explosions, volcanoes, earthquakes, and a variety of other phenomena”.
The team were most interested in the behaviour of the dominant pressure wave produced by the eruption – a type of atmospheric wave called a Lamb wave. These are longitudinal pressure waves, like sound waves, but are of incredibly low frequency.
“Lamb waves are rare; we have very few high-quality observations of them,” says Fee.
The number of Lamb waves they detected is approximately the same as was observed during the Krakatoa eruption in 1883, but this time with a much larger, higher quality dataset.
“We have more than a century of advances in instrumentation technology and global sensor density,” Matoza says. “So the 2022 Hunga event provided an unparalleled global dataset for an explosion event of this size.”
They also found that the Lamb wave reached into Earth’s ionosphere, rising at over 1,100 kilometres per hour to an altitude of about 450 kilometres.
Lamb waves caused weather disturbances in space
The Geophysical Research Letters study has analysed data from NASA’s Ionosphere Connection Explorer (ICON) mission and the European Space Agency’s (ESA) Swarm satellites. It found that cyclone-speed winds and unusual electric currents formed in the ionosphere in the hours following the eruption.
The ionosphere is the Earth’s electrified upper atmospheric layer at the edge of space.
“The volcano created one of the largest disturbances in space we’ve seen in the modern era,” says lead author Brian Harding, a physicist at University of California, Berkeley, US. “It is allowing us to test the poorly understood connection between the lower atmosphere and space.”
The Lamb waves caused strong winds to expand upwards which, as they propagated into thinner atmospheric layers, began to move faster and affect the electric currents present there.
Particles in the ionosphere regularly form an east-west flowing electric current – called the equatorial electrojet – but after the eruption this surged to five times its normal peak power and then dramatically flipped direction to flow westward for a short period of time.
“It’s very surprising to see the electrojet be greatly reversed by something that happened on Earth’s surface,” says co-author Dr Joanne Wu, a physicist at UC Berkeley. “This is something we’ve only previously seen with strong geomagnetic storms, which are a form of weather in space caused by particles and radiation from the Sun.”
These findings are adding to scientists’ understanding of how the ionosphere is affected by events on the ground as well as from space.
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