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posted by chromas on Friday December 13 2019, @08:17PM   Printer-friendly
from the electrifying dept.

Lightning is such a common phenomenon that people often overlook just how powerful it is (provided it doesn't hit you, obviously). But over the past decade, research has gradually revealed just how extreme lightning is. This everyday phenomenon is powerful enough to produce antimatter and transform atoms, leaving a radioactive cloud in its wake. Understanding how all of this happens, however, is a real challenge, given just how quickly multiple high-energy events take place.

Now, researchers have used an instrument attached to the International Space Station to track the physical processes that are triggered by a lightning strike. The work tracks how energy spreads out from the site of a lightning bolt into the ionosphere via an electromagnetic pulse.

The work relies on a piece of hardware called the Atmosphere–Space Interactions Monitor (ASIM), an ESA-built instrument attached to its lab module on the International Space Station. It's an impressive piece of hardware, tying together two X-ray/gamma-ray detectors, three UV detectors, two optical-wavelength light meters, and two high-speed cameras.

[...] A paper released by Science today describes ASIM's imaging of a single lightning bolt, which took place in 2018 off the coast of Sulawesi in Indonesia. Optical activity heralded the formation of the lightning bolt and started to intensify about 200 microseconds before the gamma rays began registering in the detectors. The gamma rays were primarily in the form of a transient flash lasting about 40 microseconds, but there was a "long" tail of emissions that extended out to 200 microseconds as their energy gradually declined.

UV light started arriving right at the same time that the gamma-ray burst hit. The initial UV light was produced by ionized oxygen as the lightning bolt moves through the atmosphere. But the UV shifted to what's called an "elve," which is a different phenomenon entirely. In the case of elves, the light is the result of an electromagnetic pulse produced by the lightning bolt itself. This travels into the ionosphere, a sparse layer of ionized gasses that starts about 100km above Earth and extends up to roughly where the ISS orbits. Because the pulse takes time to reach the ionosphere, there's a delay between the lightning and the appearance of the elve.

In this case, that delay was about 10 milliseconds, but the elve persisted for a while. That's because the pulse spreads like a balloon being inflated, tracing out an expanding sphere above the Earth. Different areas of the ionosphere get excited as the sphere makes its way through, ultimately causing UV emissions to extend over an area of up to 800 kilometers.

All of this took place in under 300 milliseconds.

Science, 2019. DOI: 10.1126/science.aax3872 (About DOIs).


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  • (Score: 0) by Anonymous Coward on Friday December 13 2019, @11:46PM

    by Anonymous Coward on Friday December 13 2019, @11:46PM (#931868)

    ...in a vacuum [nature.com]