Akademik

(jy.GAN.tik jet)

n.

A massive lightning flash that extends from the top of a thundercloud up to the ionosphere.

Han-Tzong Su of National Cheng Kung University of Taiwan and his colleagues report in the June 25 Nature that they've observed another new type of lightning — "gigantic jets." The researchers used low-light cameras to capture images of the gargantuan electrical discharges shooting upward from the tops of thunderclouds over the south china sea. The jets ascend to the ionosphere — the charged portion of the upper atmosphere — to form vast 50-mile-tall shapes resembling carrots or trees that last less than a second. By feeding negative charge from the thundercloud to the ionosphere, the researchers believe such jets may have a strong influence on what they call "earth's global electric circuit."

— Agnieszk A. Biskup, "New Lightning Discovered," The Boston Globe, July 1, 2003

Su noted that while the other types of jets seem to occur over most parts of the world, the six gigantic optical jets observed so far have all been connected to thunderstorms over the open sea.

"It is likely that the gigantic jets are a special feature of oceanic thunderstorms," he said.

In addition to the images, Su's team used data from monitoring stations in Antarctica and Japan to show that the discharges also produced extremely low frequency radio waves that could interfere with global radio communications.

Victor Pasko, an electrical engineer at Pennsylvania State University who pioneered study of blue jets, noted in an accompanying Nature commentary that in addition to causing significant disturbances of long-range radio signals, "the ionization created by a gigantic jet is likely to have a significant chemical effect on that part of the atmosphere," although no studies have been done on such changes.

— Lee Bowman, "Some lightning jets shoot up high into atmosphere," Scripps Howard News Service, June 25, 2003

Here we report observations of five gigantic jets that establish a direct link between a thundercloud (altitude 16 km) and the ionosphere at 90 km elevation. Extremely-low-frequency radio waves in four events were detected, while no cloud-to-ground lightning was observed to trigger these events. Our result indicates that the extremely-low-frequency waves were generated by negative cloud-to-ionosphere discharges, which would reduce the electrical potential between ionosphere and ground. Therefore, the conventional picture of the global electric circuit needs to be modified to include the contributions of gigantic jets and possibly sprites.

— H. T. Su et al., Gigantic jets between a thundercloud and the ionosphere," Nature, June 26, 2003

A gigantic jet is an example of a superbolt, a lightning flash that extends for tens of miles. Another example is the sprite mentioned in the example citation, which is usually called a red sprite. Both are forms of upward lightning that starts from the cloud tops and extends into the upper atmosphere. Other lightning types have equally whimsical names: carrot sprites, angel sprites, blue jets, elves, and trolls. Scientists group all of these lightning types under the heading of Transient Luminous Events (TLEs) because they appear and disappear in a few hundredths or thousandths of a second.