Earth’s atmosphere contains some powerful phenomena, and not just storms like hurricanes or blizzards. For example, Earth’s upper atmosphere features a fascinating phenomenon known as equatorial plasma bubbles. These lower-density pockets reside in Earth’s ionosphere – starting roughly 50 miles (80 km) above Earth’s surface – in the region wrapping above Earth’s equator. The bubbles aren’t visible to human eyes. But they can pose risks to aircraft communications and ultimately passenger safety. Scientists from the Hong Kong Polytechnic University said in a news release at Eurekalert on December 11, 2024, that they’ve developed a new 3D model related to these equatorial plasma bubbles. They’re trying to determine just how the bubbles disrupt navigation in aviation. And they’re trying to make aircraft systems more resilient to this type of interference.
Lead researcher Yiping Jiang of the Hong Kong Polytechnic University said in EurekaAlert:
Our model provides a comprehensive assessment of the risks posed by equatorial plasma bubbles, which is essential for improving the safe operation of ground-based systems in areas affected by these ionospheric disturbances. This research is a crucial step forward in enhancing aviation safety, particularly in regions like Hong Kong, where equatorial plasma bubbles are a frequent concern.
The researchers published their peer-reviewed study in the journal Satellite Navigation on December 2, 2024.
Equatorial plasma bubbles are an atmospheric feature that occur at night above and around the Earth’s magnetic equator. The magnetic equator is tilted just a bit from the geographic equator. So, these features are more common above the part of Earth’s surface on and near the equator.
Equatorial plasma bubbles form high up above Earth’s surface within the ionosphere, a layer of the atmosphere vital to aircraft communications. The ionosphere takes its name from the fact that the atmosphere and molecules here are ionized by solar radiation. That means an atom or molecule gains a positive or negative charge. The ionosphere plays a role in the movement of radio signals. This part of the atmosphere reflects high-frequency (HF) radio waves, enabling long-range communication between aircraft, especially over oceans, where line-of-sight communication isn’t possible. The ionosphere lets radio signals “bounce” back to Earth beyond the horizon. So the ionosphere is key to long-distance communication between aircraft and the ground.
After the sun sets on a given part of Earth, ionization in Earth’s upper atmosphere decreases dramatically. No sunlight, no ionization. And that’s when the equatorial plasma bubbles form. As positive and negative ions recombine, they create a layer of lower-density air. This less-dense air layer rises through more heavily ionized layers above, due to convection (the same process that creates bubbles in a pan of boiling water). The rising motion in Earth’s upper air creates a turbulent, bubble-like structure.
Equatorial plasma bubbles can be quite large, some 62 miles (100 km) in scale. And equatorial plasma bubbles can form throughout the year. For example, they’re common in Northern Australia from February to April and August to October.
Equatorial plasma bubbles can change the movement of radio signals, resulting in communication delays. For example, the Global Positioning System (GPS) is a space-based radio-navigation system. People use it for aviation and other navigation. It normally provides a 3D position to meter-level accuracy and time to the 10-nanosecond level. This coverage is at all times of the day and night and anywhere on Earth. But the presence of equatorial plasma bubbles affects GPS location and time accuracy. These bubbles can disable radio communications and lower GPS performance.
Equatorial plasma bubbles can also affect the ability of ground-based augmentation systems, like receivers and antennas at airports. They interrupt GPS location measurements that ensure safe, precision flight operations. Air traffic controllers and pilots use ground-based augmentation systems to correct and improve the accuracy of aircraft GPS positioning in the vicinity of airports. Computer systems onboard aircraft receive both GPS signals and ground-based corrections. These ground-based systems provide support for aircraft moving from open airspace to precision approach and landing. GPS disruptions have the potential to impact this fine-tuned process.
What the researchers found is that these ground-based systems can maintain their integrity when equatorial plasma bubbles disrupt their signals. So current systems remain useful in detecting and mitigating against the communication delays caused by equatorial plasma bubbles. Effective monitoring to detect and reduce potential communication delays caused by equatorial plasma bubbles can ensure continued effectiveness of aircraft navigation systems in these equatorial regions.
Equatorial plasma bubbles are not a direct threat to people. But the world’s reliance on radio-based technology makes them relevant to aviation safety. And the study’s authors hope their new 3D model will help in practical applications, so that aviation systems can continue to meet the highest safety standards worldwide.
Bottom line: Equatorial plasma bubbles are pockets of low density in the Earth’s ionosphere in regions around the equator. They pose risks to aircraft by disrupting radio-based navigation systems. However, research shows that while equatorial plasma bubbles can be disruptive, ground-based systems are still useful in limiting effects on aviation activities.
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