Remember the huge Tonga eruption in the South Pacific in January 2022? This underwater volcano sent tons of ash into the air. It also blew 146 teragrams of water into our atmosphere and the effect of the explosion reached space. It also made life very difficult for people on Tonga, wiping out their communications and sending tsunamis across the South Pacific.
Now, scientists report that it also sent an air pressure wave that produced a bubble of plasma in the ionosphere. That was enough to disrupt satellite communications around the world long before the pressure wave arrived.
For a team of researchers at Nagoya University in Japan, the Tonga event was a unique opportunity. It provided a chance to study the link between the atmosphere and terrestrial events such as volcanic eruptions. The team used satellites to detect the growth of equatorial plasma bubbles (EPBs). Among other things, these EPBs can disrupt radio communications and degrade GPS signals.
EPBs form when plasma, electric fields, and neutral winds move through the ionosphere. Essentially, these bubbles are localized density gradients of plasma. Atmospheric waves disturb them. Since the volcanic blast created such a wave, the team theorized that a volcanic eruption is a trigger. The Hunga Tonga-Hunga Ha’apai event was essentially a “volcanic hammer”. It pounded ten cubic kilometers of rock out in the form of ash and sediment from beneath the ocean waves. It was the biggest submarine eruption in known history.
Ionospheric Implications of the Tonga Eruption
Atsuki Shinbori and Yoshizumi Miyoshi used data from the Arase and Himawari-8 satellites to study air pressure waves from the eruption. They coordinated that with ground-based observations of something called the “total electron density” in the ionosphere. In that data, they were able to pinpoint an irregular structure of higher electron density across Earth’s equator. It occurred after the arrival of pressure waves from the eruption. “The results of this study showed EPBs generated in the equatorial to low-latitude ionosphere in Asia in response to the arrival of pressure waves caused by undersea volcanic eruptions off Tonga,” Shinbori said.
They also spotted something unusual. “Our new finding is that the ionospheric disturbances are observed several minutes to hours before the initial arrival of the shock waves triggered by the Tonga volcanic eruption,” Shinbori said. “This suggests that the propagation of the fast atmospheric waves in the ionosphere triggered the ionospheric disturbances before the initial arrival of the shock waves. Therefore, the model needs to be revised to account for these fast atmospheric waves in the ionosphere.”
Revising a Model?
This has important implications. It suggests that the long-held model of geosphere-atmosphere-cosmosphere coupling needs updating. The model says that ionospheric disturbances should only happen after the eruption. In addition, it now appears that the EPBs related to the eruption extended far beyond what people expect. “Previous studies have shown that the formation of plasma bubbles at such high altitudes is a rare occurrence, making this a very unusual phenomenon,” Shinbori said.
“We found that the EPB formed by this eruption reached space even beyond the ionosphere, suggesting that we should pay attention to the connection between the ionosphere and the cosmosphere when an extreme natural phenomenon, such as the Tonga event, occurs.”
Links to Spaceweather and Disaster Planning
Huge eruptions like the Tonga event, or space weather storms after coronal mass ejections offer new views of how our planet’s ionosphere reacts to such stressful occurrences. Essentially, a hole forms in the atmosphere. What would happen if such an event occurred during a space weather outburst? Shinbori suggests that disaster planners take them into account. “Such cases have not been incorporated into space weather forecast models,” he said. “This study will contribute to the prevention of satellite broadcasting and communication failures associated with ionospheric disturbances caused by earthquakes, volcanic eruptions, and other events.”
Key to such planning is a better understanding of our ionosphere—which we depend on for communications. The ionosphere is a region of the Earth’s upper atmosphere. It’s where solar radiation ionizes molecules and atoms. That creates positively charged ions. The area with the highest concentration of these ionized particles is called the F-region, an area 150 to 800 km above the Earth’s surface. This area of the atmosphere plays a crucial role in long-distance radio communication, reflecting and refracting radio waves used by satellite and GPS tracking systems back to the Earth’s surface. Strong solar storms can disrupt the F-region. It’s happened in the past, and will continue to do so, especially during times of maximum solar activity (called “solar max”.)
It could be doubly disastrous if a volcanic eruption, for example, affects the ionosphere the way the Tongan eruption did. Theoretically, the damage to communications could be severe. That’s why Professor Shinbori calls for the addition of volcanic eruption effects on space weather disaster planning.
For More Information
Eruption of Tonga Underwater Volcano Found to Disrupt Satellite Signals Halfway Around the World
Generation of Equatorial Plasma Bubble After the 2022 Tonga Volcanic Eruption
Tonga Eruption Blasted Unprecedented Amount of Water Into Stratosphere