An elusive atmospheric wave was detected during the Tonga volcano eruption

The catastrophic eruption of the Hunga Tonga–Hunga Haʻapai volcano in 2022 triggered a peculiar atmospheric wave that has eluded detection for the past 85 years. Researchers from the University of Hawaiʻi at Mānoa, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), and Kyoto University drew on state-of-the-art observational data and computer simulations to discover the existence of Pekeris waves — fluctuations in air pressure, which was theorized in 1937 but to date has never been proven to occur in nature.

The study was published in Journal of Atmospheric Sciences.

The South Pacific eruption earlier this year triggered what is likely the most powerful explosion the world has seen since Indonesia’s famous 1883 eruption of Mt Krakatau. The rapid release of energy triggered pressure waves in the atmosphere that quickly spread around the world.

The atmospheric wave pattern near the eruption was quite complicated, but thousands of miles away, the disturbances were led by an isolated wavefront that propagated horizontally at more than 650 miles per hour as it propagated outward. The barometric perturbations associated with the initial wavefront were clearly visible on thousands of barometric records around the world.

“The same behavior was observed after the Krakatoa eruption, and in the early 20th century, the English scientist Horace Lamb developed a physical theory for this wave,” said Kevin Hamilton, professor emeritus of atmospheric sciences at the UH Mānoa School of Ocean and Earth Sciences and Technology .

“These movements are now known as Lamb waves. In 1937, the American-Israeli mathematician and geophysicist Chaim Pekeris extended Lamb’s theoretical treatment and concluded that a second wave solution with a slower horizontal velocity should also be possible. Pekeris tried to find evidence of its slower wave in the pressure observations after the Krakatoa eruption, but could not provide convincing evidence.

Successfully identify the wave

Scientists applied a wide range of tools now available, including geostationary satellite observations, computer simulations and extremely dense networks of air pressure observations, to successfully identify the Pekeris wave in the atmosphere after the Tonga eruption.

Lead author Shingo Watanabe, deputy director of the Environmental Modeling Research Center of the Japan Marine Earth Science and Technology Agency, ran computer simulations of the response to the Tonga eruption.

“When we examined the computer-simulated and observed pulses across the entire Pacific basin, we found that the slower wavefront could be seen over wide regions and that its properties were consistent with those predicted by Pekeris nearly a century ago,” Hamilton said.