| Summary: | <p>The January 2022 Hunga Tonga–Hunga Ha&#x02BB;apai eruption was one of the most explosive volcanic events of the modern era<sup>1,2</sup>, producing a vertical plume which peaked > 50km above the Earth<sup>3</sup>. The initial explosion and subsequent plume triggered atmospheric waves which propagated around the world multiple times<sup>4</sup>. A global-scale wave response of this magnitude from a single source has not previously been observed. Here we show the details of this response, using a comprehensive set of satellite and ground-based observations to quantify it from surface to ionosphere. A broad spectrum of waves was triggered by the initial explosion, including Lamb waves<sup>5,6</sup> propagating at phase speeds of 318.2±6 ms<sup>-1</sup> at surface level and between 308±5 to 319±4 ms<sup>-1</sup> in the stratosphere, and gravity waves<sup>7</sup> propagating at 238±3 to 269±3 ms<sup>-1</sup> in the stratosphere. Gravity waves at sub-ionospheric heights have not previously been observed propagating at this speed or over the whole Earth from a single source<sup>8,9</sup>. Latent heat release from the plume remained the most significant individual gravity wave source worldwide for >12 hours, producing circular wavefronts visible across the Pacific basin in satellite observations. A single source dominating such a large region is also unique in the observational record. The Hunga Tonga eruption represents a key natural experiment in how the atmosphere responds to a sudden point-source-driven state change, which will be of use for improving weather and climate models.</p>
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