An international team used ground-based and satellite ionosphere observations to demonstrate that an air pressure wave from volcanic eruptions can produce an equatorial plasma bubble (EPB) in the ionosphere, severely disrupting satellite-based communications. Their findings have been published in the journal Scientific reports.
The ionosphere is the region of Earth’s upper atmosphere where molecules and atoms are ionized by solar radiation, producing positively charged ions. The region with the highest concentration of ionized particles is called the F region, which is an area from 150 to 800 kilometers above the Earth’s surface. The F-zone plays an important role in long-distance radio communications, as it reflects and refracts radio waves used by satellite tracking and global positioning systems back to the Earth’s surface.
These important transport processes can be disrupted by irregularities in the F-region. During the day, the ionosphere is ionized by the sun’s ultraviolet rays, creating a thick gradient of electrons with higher densities near the equator. However, perturbations that occur in this, such as plasma motion, electric fields, and neutral winds, can cause the formation of localized irregularities of the enhanced plasma density. This area can grow and develop, creating a bubble-like structure called the EPB. EPB can delay radio waves and reduce GPS performance.
Because these intensity gradients can be affected by atmospheric waves, it has long been hypothesized that they are formed by terrestrial events such as volcanic activity. For an international team led by Associate Professor-designate Atsuki Shinbori (Ho, Ho) and Professor Yoshizumi Miyoshi (Ho, Ho) of the Institute for Research in Space and Earth Environment (ISEE), Nagoya University, in collaboration with NICT, University of Electro-Communications, Tohoku University, Kanazawa University, Kyoto University, and ISAS The eruption of the Tongan volcano provided them with the perfect opportunity to test this theory.
The eruption of the Tonga volcano was the largest volcanic eruption in history. This allowed the team to test their theory by using the Arase satellite to detect EPB repeats, the Himawari-8 satellite to verify the initial arrival of air pressure waves and ground-based ionospheric observations to track the movement of the ionosphere. They observed an irregular structure of electron density across the equator that occurred after the arrival of pressure waves from the volcanic eruption.
“The results of this study showed that EPB particles were generated in the ionosphere in the equator to low latitudes of Asia in response to the outflow of pressure waves caused by the undersea volcanic eruptions off Tonga,” Shinburi said.
The group also made a surprising discovery. For the first time, they showed that ionospheric fluctuations begin a few minutes to a few hours before the atmospheric pressure waves involved in generating plasma bubbles. This could have important implications because it indicates that the long-running model of atmosphere-atmosphere-atmosphere coupling, which states that ionospheric perturbations occur only after the explosion, needs revision.
“Our new finding is that the ionic disturbances were observed several minutes to hours before the initial arrival of the shock waves from the Tonga eruption,” Shinburi said. “This indicates that the propagation of fast atmospheric waves in the ionosphere caused disturbances in the ionosphere before the initial arrival of the shock waves. Therefore, the model needs to reconsider accounting for these fast waves in the ionosphere.”
They also found that the electric parking brake extended further than standard models expected. “Previous studies have shown that the formation of plasma bubbles at such high altitudes is rare, which makes this a very unusual phenomenon,” Shinburi said. “We found that the EPB formed by this volcanic eruption reached space even beyond the ionosphere, which indicates that we should pay attention to the relationship between the ionosphere and the atmosphere when an extreme natural phenomenon occurs, such as the Tonga event.”
“The results of this research are important not only from a scientific point of view but also from a space weather and disaster prevention point of view,” he said. “In the event of a large-scale event, such as the eruption of the Tonga volcano, observations have shown that a hole in the ionosphere can form even under conditions that are likely to occur under normal conditions. Such cases have not been integrated into space weather forecast models. This study will contribute in preventing satellite transmissions and communications failures associated with ionospheric disturbances caused by earthquakes, volcanic eruptions, and other events.”
Generating a tropical plasma bubble after the 2022 eruption of the Tonga volcano, Scientific reports (2023). DOI: 10.1038/s41598-023-33603-3
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