A gigantic blue jet emerging from a storm cloud has been mapped in 3D

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Un jet bleu a été capturé par un photographe amateur au-dessus d'un nuage d'orage. © Matthew Griffiths

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[EN VIDÉO] Discovering the hidden side of storms As spectacular as they are mysterious, sprites belong to the family of transient light phenomena (TLE). During violent storms, lightning sometimes heads upward and tickles the ionosphere, at an altitude of nearly 80 kilometers. They are nicknamed the “blue jets”. In even rarer cases, these planes are much more gigantic than others. Although they are particularly difficult to detect, in a study published in the journal Science Advances, researchers benefited from a stroke of fate and managed to map this event! The electrical shock occurred in Oklahoma where a plane was captured by a hobbyist photographer, but it turns out that two NOAA weather radars and geostationary environmental satellites were located nearby. Thanks to the data collected by these instruments, the team was able to gather enough data to characterize the jet. “This is probably the first time that a giant jet has been mapped in three dimensions above clouds” The fact that the giant jet detected by several systems, including the Lightning Mapping Array and two geostationary optical lightning instruments, was a unique event and we gives a lot more information about giant jets,” enthused Doug Mach, co-author of the study and a member of the University Space Research Association. (USRA). “The most important thing is that this is probably the first time that ‘has mapped a gigantic jet in three dimensions above the clouds with all the Geostationary Lightning Mapper (GLM) instruments. “Carries 100 times more electrical charge than normal lightning In total, the researchers measured that the bolt sent nearly 300 coulombs of electrical charge into the ionosphere, compared to a typical cloud-to-ground or intracloud lightning typically carrying less than 5 coulombs . per second.) But how do they form? In their study, the researchers noted that “most giant jets emanate from tropical maritime environments, typically over the ocean and at low latitudes, during the hurricane season when temperatures of the ocean surface are warm. Parent storms typically have high cloud tops (15–18 km a.s.l.), often above the tropopause, which is a characteristic of severe convection. There is no choice but to evacuate to the top in this case. In fact, they observed a decrease in lightning a few minutes before the gigantic upward discharge. “For some reason, there’s usually a suppression of cloud discharges to the ground,” explained Levi Boggs, first author of the study and a researcher at the Georgia Tech Research Institute (GTRI). upper part of the storm weakens the upper layer of charge, which is usually positive. In the absence of the lightning discharges that we normally see, the giant jet can relieve the accumulation of excessive negative charges in the cloud.” parts, similar to those of classical lightning: a main band called the leader is at a temperature of almost 4,500 ° C. and ionizing the surrounding oxygen and nitrogen, and at their ends, several small coils of cold plasma (called serpentines in the paper) at about 200 ° C and ionizing only nitrogen. They propagate into the lower ionosphere at an altitude of 50-60 miles (about 80-90 km), making a direct electrical connection between the tops of the clouds and the lower ionosphere, which is the lower edge of space. But also, the surrounding radio antennas picked up signals from very high-frequency (VHF), which the researchers tried to figure out. The data showed that as the discharge rises to the top of the cloud and then into the ionosphere, these high-frequency signals are detected at altitudes ranging from enter and the 22 and 45 kilometers. In contrast, the optical signals from the flashes are more likely between 15 and 20 kilometers. The received radio signals therefore correspond more to the streamers, the cold plasma streamers, which are at the tip of the lightning. “The optical and VHF signals definitively confirmed what researchers had suspected but not yet proven: VHF lightning radio is emitted from small structures called streamers that sit at the tip of the developing lightning, while the current stronger electrical current flows significantly behind it, peaking in an electrically conductive channel called the leader,” said study co-author Steve Cummer, a professor of electrical and computer engineering at Duke University. Jets pose problems for the operation of satellites in low orbit, and even for transmission. over-the-horizon radars, which also use radio waves. By better understanding the physics taking place inside these extreme light transients, researchers hope to be able to protect these devices in the future. Interested in what you just read?
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