A giant blue jet has been mapped in 3D

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[EN VIDÉO] Discovering the hidden side of the storm
Spectacular as they are mysterious, sprites belong to the family of transient light phenomena (TLE).

time’lightning Violent, lightning sometimes goes overhead and comes to ticklethe ionosphere, about 80 km above sea level. They are nicknamed “Blue Jets”. Even in rare cases, these jets can be much more massive than others. Although they are particularly difficult to detect in a study published in the journal Science advances, the researchers benefited from a stroke of luck and went so far as to map such a phenomenon! Oklahoma where the electric shock occurred A jet has been captured By an amateur photographer.

However, it so happened that, close to this location, there were two meteorological radars and a geostationary environmental satellite. NOAA. Using the data collected by these instruments, the team was able to collect enough data to identify the jet.

This is possibly the first time that a giant jet has been mapped in three dimensions above a cloud

“The massive jet was detected by several systems, including the Lightning Mapping Array and two instruments. the thunder Geostationary optics, was a unique phenomenon and gives us much more information about the massive jet”, Encouraged Doug Mach, study co-author and memberUniversity Space Research Association (USRA).

“Most importantly, this is perhaps the first time a massive jet has been mapped in three dimensions above the cloud with the Geostationary Lightning Mapper (GLM) instrument set.”

It carries 100 times more electrical charge than normal lightning

In total, the researchers measured that the jet sent about 300 Coulomb of electric charge in the ionosphere, while a Flash Classical or intra-cloud between cloud and ground typically carries less than 5 coulombs. The process is similar, however: a negative charge in the cloud is moved outward, except that, in the case of a jet, it is by several thousandths of current.amps (One ampere corresponds to one coulomb per second).

But how are they formed? In their study, the researchers noted that “ Most giant jets originate in the marine tropical environment, usually over and under the ocean latitudethe time season of hurricane As sea surface temperatures warm. Parent thunderstorms typically have high cloud tops (15–18 km asl), often crossing the tropopause, which is a characteristic of movement strict”.

Then, according to them, something below or inside is blocking the flow of charge storm clouds. In this case there is no other option but to move to the top. They actually observed a decrease in lightning minutes before the massive discharge moved upward. “For some reason, cloud-to-ground emissions are generally suppressed.”Levi Boggs, the study’s first author and researcher, explained Georgia Tech Research Institute (GTRI).

“There’s a buildup of negative charge, and then we think the storm top conditions are weakening the top charge layer, which is usually positive. Absent the lightning discharge that we normally see, the massive jet could release excess negative charge from building up in the cloud.”

Microstructure in massive jets

Among the jets that the researchers characterized, they distinguished different parts, such as Classic buzz : is called a principal band the leader At a temperature of about 4,500 degrees Celsius and ionizes oxygen andNitrogen Around and at its edge, several small streamers of cold plasma (called Streamer in the article) at a temperature of about 200 °C and only nitrogen ions are ionized.

“Detailed data shows that these cold streamers begin their propagation just above the cloud topsL. Boggs explained. They propagate in the lower ionosphere at altitudes of 50 to 60 miles (about 80-90 km), Establishing a direct electrical connection between the cloud tops and the lower ionosphere, which is the lower edge of space. »

But also, the antenna Radio Picks up very high frequency signals around (VHF), which researchers have tried to understand. The data thus show that the discharge rises to the top of the cloud, then in the ionosphere, these high-frequency signals are detected at altitudes ranging from 22 to 45 km. Conversely, the optical signals of flashes are between 15 and 20 km.

The received radio signal is therefore more similar to the streamer, its streamers Cold plasmaWhich is the tip of the lightning. “The VHF and optical signals confirmed what researchers suspected but had not yet proven: VHF lightning is emitted from small structures called radio streamers that sit at the front of lightning, when Electric power The strongest conducts significantly behind it, peaking in an electrically conductive channel called the leader”Steve Comer, co-author and professor of electrical and computer engineering at Duke University.

These are emissions Radio from jets creates problems for satellite operations orbit Less so, even for trans-horizon radars, which also use radio waves. Through better understanding the physical That takes place in this Luminous transients In the extreme, researchers hope to be able to protect these devices in the future.

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