Picture this: you’re thousands of kilometers above the Earth’s surface, in the ionosphere – the uppermost layer of our planet’s atmosphere. Here, atoms and molecules are consistently getting ionized due to constant exposure to solar radiation, giving birth to an abundance of positively charged ions.
This part of the atmosphere, known as the F-region, becomes a vital cog in the mechanism of long-distance radio communication, allowing the reflection and refraction of radio waves used by satellite and GPS tracking systems back to Earth’s surface. But the F-region isn’t static. Changes in this area can cause severe disruption in these vital communications.
The stability of the F-region is a delicate dance of intricate balance. As the Sun’s ultraviolet radiation ionizes the ionosphere during the day, an electron density gradient forms, with the highest density found near the equator.
However, various disruptors such as the movement of plasma, electric fields, and neutral winds can distort this gradient. These disruptions can lead to the creation of a localized irregularity in plasma density, which, when amplified, forms a bubble-like structure termed an equatorial plasma bubble, or EPB.
The impact of an EPB on radio communication is nothing short of disastrous – it delays radio waves and significantly deteriorates GPS performance.
Atmospheric waves can meddle with these density gradients, sparking a longstanding hypothesis that these waves could be triggered by terrestrial events, like volcanic eruptions. Recently, this theory was put to the test by an international team of researchers led by Professor Atsuki Shinbori and Professor Yoshizumi Miyoshi from the Institute for Space–Earth Environmental Research (ISEE) at Nagoya University.
The team collaborated with several renowned institutions, including NICT, The University of Electro-Communications, Tohoku University, Kanazawa University, Kyoto University, and ISAS. Their opportunity? The Tonga volcano eruption – the biggest submarine eruption in recorded history.
The team capitalized on this event, using the Arase satellite to detect EPB occurrences, the Himawari-8 satellite to track the initial arrival of air pressure waves, and ground-based ionospheric observations to trace the movement of the ionosphere.
Their observations unveiled an irregular structure in the electron density across the equator that came into existence following the arrival of pressure waves generated by the volcanic 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,” stated Shinbori.
The study led to another striking revelation. Contrary to the long-held model geosphere-atmosphere-cosmosphere coupling that suggests ionospheric disturbances only occur after the eruption, the team discovered that ionospheric fluctuations start a few minutes to a few hours before the arrival of atmospheric pressure waves that generate plasma bubbles.
This discovery nudges the scientific community to reconsider the existing model and could potentially reshape our understanding of the atmospheric-ionospheric relationship.
The findings have been meticulously compiled and published in the journal Scientific Reports. These discoveries could be monumental in predicting the effects of terrestrial events on our satellite-based communication systems.
“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.”
The research team also found that the EPB extended much further than standard models had predicted.
“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.”
“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.”
Equatorial plasma bubbles (EPBs), also known as equatorial ionospheric irregularities, are a phenomenon that primarily occurs in the F-region of the Earth’s ionosphere, a layer in the upper atmosphere that is ionized by solar radiation.
These structures, often described as “bubble-like,” can play a significant role in disrupting communications systems that rely on ionospheric radio wave propagation, such as GPS tracking and satellite-based communication systems.
EPBs are typically observed in the post-sunset period and extend from the equatorial region towards higher latitudes. During the day, the ionosphere is bombarded by the sun’s ultraviolet radiation, creating a density gradient of electrons, with the highest concentration near the equator. But this stable condition can change.
Disruptions, such as moving plasma, electric fields, and neutral winds, can lead to the creation of localized irregularities in plasma density. Over time, these irregularities can grow and evolve into EPBs. They appear like tube-like structures extending along the Earth’s magnetic field lines, with the ’empty’ or ‘bubble’ part representing regions of depleted electron density.
The development of these bubbles can cause significant disruption in radio communications. They distort the path of the radio signals as they travel through the ionosphere, leading to scintillations or rapid variations in amplitude and phase of the signals. This effect can lead to significant issues for GPS receivers, causing errors in positioning or even loss of lock on the signal.
Research has suggested that atmospheric waves, possibly triggered by terrestrial events like earthquakes and volcanic eruptions, can affect the electron density gradient in the ionosphere, leading to the formation of EPBs.
However, our understanding of the formation, evolution, and dynamics of EPBs is still evolving. Scientists use a variety of techniques, including satellite observations, ground-based radar, and advanced computational modeling, to study these complex phenomena and to better predict their occurrence and potential impacts on communication systems.
Image Credit: NOAA/ NASA