The eruption of Tonga’s Hunga Tonga-Hunga Ha’apai volcano earlier this year sent atmospheric waves 300km above the Earth’s surface, causing disturbances similar to those created by “severe solar storms”, scientists have said.
Earlier studies had revealed that the volcanic eruption, which triggered a tsunami, was about a thousand times more powerful than the atomic bomb dropped by the US on Hiroshima during the Second World War.
Researchers had previously found that the ash from the volcanic eruption, which cut off Tonga’s communications from the rest of the world, reached into the Earth’s mesosphere – the third layer of atmosphere, between the stratosphere and the thermosphere. The mesosphere extends from about 50km to 85km above the planet.
In the new study published on Wednesday in the journal Frontiers in Astronomy and Space Sciences, scientists assessed data recorded by 5,000 global navigation satellite system ground receivers located around the globe.
Researchers, including those from MIT in the US, observed substantial evidence of eruption-generated atmospheric waves and their imprints on the Earth’s ionosphere, 300km above the planet’s surface, over an extended period.
These waves were active for at least four days after the eruption and circled the globe three times, scientists said, adding that the ionospheric disturbances passed over the US six times, “at first from west to east and later in reverse”.
The findings shed light on as yet unknown ways in which atmospheric waves and the global ionosphere are connected.
“This study provides substantial first evidence of their long-duration imprints up in the global ionosphere,” the scientists wrote.
Scientists said the disturbances could be due to Lamb waves – named after mathematician Horace Lamb – which travel at the speed of sound globally without much reduction in amplitude.
While these are located predominantly near the Earth’s surface, they can exchange energy with the ionosphere through complex pathways, the researchers said.
“Prevailing Lamb waves have been reported before as atmospheric responses to the Krakatoa eruption in 1883 and other geohazards,” the scientists added.
Processes such as sudden energy inputs from the sun in the form of solar flares, as well as terrestrial weather, and human-made disturbances can lead to a form of space weather called travelling ionospheric disturbances (TIDs).
Only severe solar storms are known to produce TID global propagation in space for several hours, if not for days, the scientists said, adding that volcanic eruptions and earthquakes normally yield such disturbances only within thousands of kilometres.
“By detecting these significant eruption-induced ionospheric disturbances in space over very large distances, we found not only generation of Lamb waves and their global propagation over several days but also a fundamental new physical process,” study lead author Shun-Rong Zhang said in a statement.
“In the end, surface and lower atmospheric signals can make a loud splash, even deep in space,” Dr Zhang said.
