An equatorial plasma bubble (EPB), which might be caused by volcanic eruptions, could seriously interfere with satellite-based communications, according to research conducted by an international team using satellite and ground-based ionospheric measurements. Their findings were published in the journal Scientific Reports.
The area of the Earth’s upper atmosphere known as the ionosphere is where solar energy ionizes molecules and atoms, producing positively charged ions. The F-region, located 150 to 800 km above the Earth’s surface, is the region with the largest concentration of ionized particles.
Because it reflects and refracts radio waves used by satellite and GPS tracking systems back to the Earth’s surface, the F-region is essential for long-distance radio communication.
These important transmissions can be disrupted by irregularities in the F-region. The Sun’s UV rays ionize the ionosphere during the day, resulting in an electron density gradient with the maximum density close to the equator.
But obstructions to this, like plasma motion, electric fields, and neutral breezes, can result in the development of a localized irregularity with increased plasma density. This region can grow and evolve, creating a bubble-like structure called an EPB. EPB can delay radio waves and degrade the performance of GPS.
The results of this research are significant not only from a scientific point of view but also from the point of view of space weather and disaster prevention. In the case of a large-scale event, such as the Tonga volcano eruption, observations have shown that a hole in the ionosphere can form even under conditions that are considered unlikely to occur under normal circumstances. Such cases have not been incorporated into space weather forecast models. 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.
Professor Atsuki Shinbori
It has long been assumed that these density gradients are created by terrestrial events like volcanic activity because they can be influenced by atmospheric waves.
For an international team led by Designated Assistant Professor Atsuki Shinbori (he, him) and Professor Yoshizumi Miyoshi (he, him) of the Institute for Space-Earth Environmental Research (ISEE), Nagoya University, in collaboration with NICT, The University of Electro-Communications, Tohoku University, Kanazawa University, Kyoto University and ISAS, the Tonga volcano eruption offered them a perfect opportunity to test this theory.
The Tonga volcano eruption was the biggest submarine eruption in history. This gave the scientists the opportunity to test their idea using the Himawari-8 satellite to examine the initial arrival of air pressure waves, the Arase satellite to look for EPB occurrences and ground-based ionospheric measurements to monitor the ionosphere’s migration. After the arrival of pressure waves caused by the volcanic explosion, they noticed an uneven structure of the electron density over the equator.
“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.
The group also made a surprising discovery. They demonstrated for the first time that ionospheric oscillations begin many minutes to several hours before the atmospheric pressure waves responsible for plasma bubble formation.
This shows that the long-held geosphere-atmosphere-cosmosphere linkage hypothesis, which asserts that ionospheric disturbances only occur after the eruption, has to be revised, which could have significant ramifications.
“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.”
They also found that the EPB extended much further than predicted by the standard models. “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 extreme natural phenomenon, such as the Tonga event, occur.”
“The results of this research are significant not only from a scientific point of view but also from the point of view of space weather and disaster prevention,” he said. “In the case of a large-scale event, such as the Tonga volcano eruption, observations have shown that a hole in the ionosphere can form even under conditions that are considered unlikely to occur under normal circumstances. Such cases have not been incorporated into space weather forecast models. 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.”
