Thunderstorms sometimes produce gigantic jets of lightning that exit the top of the storm and connect with the lower edge of space. This one, however, was one of the most unique ever recorded.
The phenomenon of giant jets is illustrated by the analysis of a large electrical discharge rising 80 kilometers above a thunderstorm in Oklahoma.
It carried 100 times more electrical charge than typical thunderstorm lightning, making it the most powerful giant jet ever studied. It took place on May 14, 2018, in the state’s southwest.
An electrical charge moving from the storm into the ionosphere, the lower edge of space, amounted to about 300 coulombs. In most cases, lightning does not carry more than five coulombs between the cloud and the ground. Lightning leaders, which are very hot structures, over 4,426 degrees Celsius, rose with the rising discharge. Relatively cool plasma streams (approximately 200 degrees Celsius) were also present in the rising discharge.
Levi Boggs, a research scientist at Georgia Tech Research Institute (GTRI) and the paper’s corresponding author, said, “We were able to map this gigantic jet in three dimensions with very high-quality data.”
“We were able to see very high frequency (VHF) sources above the cloud top, which had never been observed before.” Using satellite and radar data, it was possible to determine where the very hot leader portion of the discharge was located above the cloud.”
Using the data from the USRA (Universities Space Research Association), co-author Doug Mach pointed out that the 3D locations for lightning’s optical emissions were well above clouds.
Mach commented that detecting the giant jet by multiple systems, including the Lightning Mapping Array and two geostationary beam-optical instruments, was an important event. Furthermore, the Geostationary Lightning Mapper (GLM) is probably the first instrument suite to map a gigantic jet above clouds dimensionally.”
Despite being observed and studied for the past two decades, giant jets have rarely been detected because there is no dedicated observing system. A colleague told Boggs about the Oklahoma event, which a citizen scientist documented on May 14, 2018, who used a low-light camera to photograph a giant jet.
It was fortunate for the event to occur near a lightning mapping system, two NEXRAD stations, and Instruments on Geostationary Operational Environmental Satellite Network satellites, in addition to being accessible to VHF lightning mapping systems near the location. GOES systems from NOAA were made available to Boggs, so he worked with colleagues to bring the data together for analysis.
As Boggs explained, detailed data showed that cold streamers spread just above the cloud’s top. Located at an altitude of 50 to 60 miles, these rays propagate to the lower ionosphere, where space’s lower edge is located. They make a direct electrical connection between the upper part of the cloud and the lower ionosphere.
In less than a second, the upward discharge transfers thousands of amps of current from the cloud to the ionosphere, as is typical for giant jets.
VHF radio sources were detected at an altitude of 22 to 45 kilometers (13 to 28 miles) as the discharge ascended from the cloud top, while optical emissions from lightning remained at an altitude of 15 to 20 kilometers (9 to 12 miles) near the cloud top.
Data indicating simultaneous 3D optical and radio detection of lightning emissions suggest that VHF lightning networks detect emissions from the corona of filamentary discharges rather than the leader channels.
According to records of the Oklahoma storm, there was little lightning activity before the giant record-breaking jet fired. Researchers believe something may be blocking the flow of charge.
“For whatever reason, there’s usually a suppression of discharges from the clouds to the ground,” Boggs said. “There’s a buildup of a negative charge, and then we think that the conditions at the top of the storm weaken the top layer of charge, which is usually positive. In the absence of the lightning discharges we normally see, the gigantic jet can alleviate the accumulation of excess negative charge in the cloud”.
As of yet, there are many questions unanswered about the giant jets, which belong to a mysterious class of transient luminous phenomena. They are rare and sometimes found by chance, either by aircraft pilots or passengers spotting them or by observers operating night-scan cameras on the ground.
Giant jets have been reported more often in tropical regions of the world than in any other region. The frequency of giant jets ranges from 1,000 to 50,000 each year. The giant jet from Oklahoma, which was twice as strong as the next strongest, did not form part of a tropical storm.
Besides their novelty, giant jets could impact the operation of satellites in low-Earth orbit, Boggs said. It is also possible that the giant jets could affect technologies such as over-the-horizon radars that bounce radio waves off the ionosphere as more space vehicles are launched. Signal degradation and performance issues may become more serious as more space vehicles are launched.
A paper on the results has been published in Science Advances.
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