Scientists have known for the last ten years or so that thunderstorms can generate brief, powerful bursts of gamma rays. These rays are so bright that they can affect instruments hundreds of miles away. Because they can originate near the same altitudes at which commercial aircraft routinely fly, scientists have been studying them to determine just how dangerous gamma ray radiation might be to crew and passengers. But the research was hampered because scientists did not know exactly how thunderstorms generate gamma rays. Now, it seems, there may be at least a few answers to that question.
Scientists at Florida Tech have created a physics-based model showing how thunderstorms product high-energy radiation. The model suggests that thunderstorms can sometimes produce a highly unusual form of electrical breakdown involving high-energy electrons and their anti-matter equivalent known as positrons. The interactions between these particles produces an explosive growth in the number of these high-energy particles, which results in the gamma ray flashes. The particles rapidly discharge the energy in the thundercloud. This phenomenon creates a kind of electrical breakdown within the storms, but produces very little light. For that reason, these gamma ray discharges are known as “dark lightning.”
How dangerous is this “dark lightning” to aircraft passengers and crew who might find themselves caught in the “wrong” thunderstorm? According to the Florida Tech researchers, passengers in aircraft flying near the tops of the storms experience radiation doses equivalent to about ten chest x-rays, or about the same amount of radiation they would receive from natural background sources over a year. But if the aircraft is near the middle of the storm, that radiation dose could be about ten times larger.
Pilots try very hard to avoid thunderstorms, but inevitably a few plans do end up flying inside electrified storms. When that happens, people may be exposed to sizable doses of radiation caused by the dark lightning. Researchers are now turning their attention to how often this might actually occur, and what the long-term effects of these high exposures might be.
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