Huge “red sprite” high in the sky
Did you know that when billowing thunderstorm clouds sweep across the sky, you may see a miraculous natural spectacle in the sky in the distance: several huge red “lightning clusters” suddenly appear and then disappear in a flash. In the past, only those who were lucky enough to see this fantastic landscape, the development of modern photography technology has allowed more people to see this shocking weather phenomenon through video data.
This magnificent Transient Luminescence (TLE) has a lively name – “Red sprites”. The size and shape of each occurrence vary greatly, with some streaking across the sky like a columnar meteor, and others stretching like tentacles of a deep-sea monster. But whatever its shape, it appears larger than a normal lightning bolt, and typically spans 50 to 90 kilometers high in the sky.
Although it is very large, its duration is shorter than that of ordinary lightning, so that for a long time, it was believed to be a human hallucination. Beginning in 1886, there have been sporadic pilot eyewitness reports of bizarre red flashes observed in high-altitude flights. But for decades after World War I, such reports were dismissed as hallucinations caused by pilots’ fears. Why do scientists make such mistakes? Because at that time, the academic community generally believed that strong atmospheric discharge activities would only occur in the troposphere—the layer closest to the ground in the atmosphere. They believed that going further up, the electricity generated in the stratosphere and the middle layer would be calm.
In 1925, the Nobel Prize winner and Scottish physicist Charles Wilson proposed that under the meteorological conditions of large-scale thunderstorms, electrical discharges may also occur in the upper atmosphere. This view broke the previous concept, but at that time, the phenomenon of “red elves” had never been recorded by human images.
Until 1989, the University of Minnesota was preparing for a rocket launch, and one of the tasks was to test low-light cameras. The test accidentally captured two bright beams of light, which became the first photo of the “Red Fairy”, which greatly stimulated the research interest of the academic community. In the following years, researchers named it the “red elf” according to its two characteristics of “glowing red” and “elusive”.
In 1994, researchers from the University of Alaska in the United States used an aircraft at an altitude of 10,000 meters to obtain a color image of a “red elf” above a thunderstorm cloud for the first time through a high-speed low-light camera and an image intensifier: a huge luminous space that occupies more than 10,000 cubic kilometers of atmosphere! As can be seen from the image, this huge red elf is mainly divided into three parts: the uppermost halo is distributed at an altitude of 88 to 95 kilometers, the red luminous body in the middle is distributed at 66 to 74 kilometers, and the tendrils below are distributed at 40 to 60 kilometers, and this flash is not as red as the whole body visible to the naked eye. Its upper part is red, turns purple downwards, and finally turns blue.
With the increase of video materials, the academic circles have done a lot of research on the “red elf”. It belongs to a kind of high-level atmospheric discharge phenomenon, which often appears on the top layer of thunderstorm clouds, which is about 30 to 90 kilometers away from the ground, and belongs to the middle and upper layers of the atmosphere. It is seen more than in extreme weather such as thunderstorms because the electromagnetic waves generated by lightning strikes expand upward and hit the ionosphere, which is a prerequisite for its appearance.
However, in thunderstorms and rainy days, “red elves” do not necessarily appear. Because when a thunderstorm cloud in the sky discharges to the ground, three phenomena will be formed: cloud lightning, cloud lightning and ground lightning. Among them, ground lightning is the discharge phenomenon between the cloud and the ground, and it is also the main cause of lightning disasters. Ground lightning can be divided into positive and negative. Only when positive ground lightning falls at a speed of 10,000 kilometers per second will a “red elf” be produced, and the probability accounts for only one-tenth of all ground lightning. In addition to the low probability of occurrence, the duration of the “red wizard” is also very short. It is a huge but weak streamer of positive polarity, which is equivalent to the aurora of medium brightness. Its “longest” duration is only tens to hundreds of milliseconds, and it disappears into the sky in the blink of an eye.
In the past, due to the low probability of occurrence and strong randomness, it was very difficult to record and image the “Red Fairy”. The high altitude of flame-like red light, or the picture of red lightning flashing like a thunderbolt is extremely rare. In recent years, with the development of science and technology, people have obtained tens of thousands of images of “red elves” from ground observation stations, aircraft, and space stations. Under the white flash of thunderstorm activity, the image of “Red Spirit” is already very clear. Gradually, people discovered that the discharge phenomenon in the high-altitude atmosphere is not only “red lightning”, but also blue jets, giant jets, and circular discharges. Throughout the ages, countless legends have been born in the human world because of these unimaginable natural wonders. They attract the unremitting exploration of human beings in the field of science to explore the endless secrets of the universe.