Source: Geophysical Research Letters
The volcanic eruption of the South Pacific Ocean’s Hunga Tonga–Hunga Ha‘apai in January 2022 unleashed a colossal amount of energy—equivalent to around 4–18 megatons of TNT, according to a preliminary estimate by NASA scientists. The underwater volcano’s explosion triggered 15-meter-high tsunami waves that battered the islands of Tonga, causing widespread destruction and at least three deaths.
The blast also extended upward—atmospheric waves produced by the eruption rippled through the ionosphere. To track the traveling ionospheric disturbances (TIDs) as they propagated across the planet, Themens et al. analyzed data from a network of more than 4,735 Global Navigation Satellite System (GNSS) receivers.
The team detected two large-scale TIDs (LSTIDs) generated from the eruption, with wavelengths greater than 1,600 kilometers (almost 1,000 miles). One had an initial speed of about 950 meters per second, which is nearly 3 times the speed of sound at Earth’s surface and close to the speed of sound in the ionosphere. The LSTIDs exhibited strong directionality—the initial wave was the dominant wave response at Hawaii to the northeast, but it was barely detectable near Australia and to the west.
In addition, the authors discovered that the explosion also produced medium-scale TIDs (MSTIDs) that continued to be produced at the eruption site for up to 6 hours. The first wave traveled at a speed of 337 meters per second and was visible at least 16,000 kilometers (nearly 9,942 miles) from the eruption site. Subsequent MSTIDs had speeds ranging from 200 to 400 meters per second. These waves didn’t demonstrate a clear directional preference and formed the dominant wave response seen globally.
According to the authors, modeling and additional measurements will further clarify the mechanisms underlying these ionospheric disturbances, especially for areas lacking GNSS stations. (Geophysical Research Letters, https://doi.org/10.1029/2022GL098158, 2022)
—Jack Lee, Science Writer