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Of all the weather phenomena that our beautiful planet throws at us, lightning is one of the most spectacular and mysterious. Even though storms do occur regularly, we still have a hard time understanding and describing their crackling electric shocks generated in the sky.
One type of lightning bolt is so strange and rare, in fact, that we didn’t even have concrete evidence of its existence until 1990, when researchers identified its “ rocket-like ” motion in a video. toured from NASA’s space shuttle the year before.
Later nicknamed “ blue jets, ” the streaks are now recognized as brilliant flashes of light that last only a few hundred milliseconds, as lightning propagates upward from clouds and into the stratosphere.
A blue jet photographed in Hawai’i. (Gemini Observatory / AURA / Wikimedia Commons)
We can’t easily see this phenomenon under a curtain of clouds – but that doesn’t mean scientists can’t observe it above them. About 400 kilometers (250 miles) above the planet orbit the International Space Station, and for some time the instruments on board have been monitoring these mysterious lightning bolts in reverse.
Now, after being installed in 2018, a European Space Station observatory equipped with optical sensors, photometers, and gamma and x-ray detectors has recorded five blue flashes from the top of a storm cloud, including the one ended with a streaked blue jet. high in the stratosphere.
These rare glimpses provide valuable insight into the appearance of the mysterious landfills, according to a team of researchers led by physicist Torsten Neubert of the Technical University of Denmark.
Blue jets are believed to be triggered when a positively charged cloud top encounters a negatively charged layer at the cloud boundary and the layer of air above. This is believed to produce a blackout that forms a leader – an invisible conductive channel of ionized air along which lightning travels.
However, our understanding of the leader of the blue jet is quite limited. This is where the data analyzed by Neubert and his team fills in the gaps.
On February 26, 2019, the ASIM (Atmosphere-Space Interactions Monitor) observatory recorded five blue flashes, of about 10 microseconds each, at the top of a storm cloud, not far from the island of Nauru in the Pacific Ocean.
One of these flashes produced a blue jet, reaching up to the stratopause – the interface between the stratosphere and the ionosphere, at an altitude of about 50 to 55 kilometers (about 30 to 34 miles).
In addition, the observatory recorded atmospheric phenomena called ELVES (abbreviation of Emission of Light and Very Low Frequency Perturbations due to Electromagnetic Pulse Sources). These are expanding rings of optical and ultraviolet emission in the ionosphere that appear above storm clouds, lasting about a millisecond, as shown in the animation below.
They are believed to be generated by an electromagnetic pulse at the bottom of the ionosphere, caused by a lightning discharge.
The leader’s red show, however, was weak and very limited. This, according to the research team, suggests that the leader itself is very short and localized, compared to fully developed lightning leaders between the ground and the clouds.
It also suggests that the flashes and the blue jet itself are a type of discharge streamer: branching, twisted sparks emerging from high-voltage sources, like Tesla coils, in a chain reaction of air particles. ionizing.
“We therefore propose that the UV pulses be elves that are generated by flash currents from streamers, rather than lightning currents,” the researchers write in their paper.
Flashes, they believe, are similar to narrow bipolar events. These are high-power radioelectric discharges that occur inside clouds during thunderstorms, which are known to trigger lightning in clouds. Blue flashes atop clouds, the team said, are likely the optical equivalent of this phenomenon and can turn into blue jets.
Since narrow bipolar events are quite common, it could mean blue lightning is more common than we thought. Knowing more about their frequency could give us a much better understanding of storms and lightning, not to mention our atmosphere and all the complex interactions within it.
The team’s research has been published in Nature.
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