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Scientists investigate 'dark lightning' threat to aircraft passengers

One stormy flight could give lifetime radiation dose

A dark lightning strike on a 737

US Navy scientists are going to rig aircraft with radiation detectors to check if a phenomenon known as dark lightning could be killing aircraft passengers.

Dark lightning is the product of the electrical activity caused by thunderstorms and produces intense bursts of omnidirectional terrestrial gamma-ray flashes (TGFs) up to half a mile wide, as electrons and positrons are forced to interact by the atmospheric disturbance such storms produce.

The recently discovered phenomenon occurs off the human visual spectrum – thus the name – and at altitudes between six and ten miles within the head of thunderstorm systems. Dark lightning may also play an important role in limiting the amount of electrostatic lightning produced by thunderstorms, but for humans the results could be deadly.

Simulations by the US Naval Research Laboratory's space science division suggest that a single flight that is hit by a TGF would give passengers and crew a lifetime's safe dose of ionizing radiation – the equivalent of hundreds of chest x-rays, thousands of flights, or tens of thousands of trips through the TSA's now defunct backscatter x-ray perv scanners.

A dark lightning strike on a 737

A simulated dark lightning strike from beneath a 737

To quantify the risk, the NRL team used the calorimeter on NASA's Fermi gamma ray space telescope to measure the energy dark lightning puts out and assess any potential risk to air travelers. This data has now been fed into a simulator looking at the effect on a Boeing 737 – and the results aren't good for the passengers.

The next stage of the research is to get instruments up into a major thunderstorm and take measurements of dark lightning in situ. In the summer the NRL will begin balloon flights into storm systems, and there are also plans for a specially-shielded aircraft to search for gamma radiation.

In the meantime, the risk to fliers is thought to be minimal. Commercial airlines avoid thunderstorms wherever possible, and the chance of accidental irradiation is unlikely to be an issue. Still, the NRL study should give a clearer idea of whether the dark lightning phenomenon is something to be seriously concerned about. ®

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