20 years ago, on the night of July 5-6, 1989, an important event took place in the history of planet Earth exploration. John Randolph Winkler, a retired professor, 73-year-old NASA veteran, pointed a high-sensitivity video camera at the storm clouds, and then, looking at the recording frame by frame, discovered two bright flashes, which, unlike lightning, did not go down to the ground, but up to ionosphere. So sprites were discovered - the largest of the high-altitude discharges in the Earth's atmosphere. They clearly confirmed the existence of a global electrical circuit on our planet and provided new opportunities for its study.
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The discharges recorded by John Winkler started from a height of 14 kilometers, and their dimensions were more than 20 kilometers. The mechanism leading to their appearance was unclear, and it took a lot of scientific courage to announce an electrical discharge rising from the borders of the troposphere to such a height.
To get more convincing evidence, an enthusiastic Winkler waited until Hurricane Hugo hit Minnesota and on the night of September 22-23 again recorded many similar high-altitude discharges over thunderclouds on video. Interestingly, he formally conducted this research as an amateur, since it was not included in any scientific programs. But Winkler, of course, was not an amateur and acted decisively, like a man clearly aware of his mission. From his past work at NASA, he has a faulty high-speed video camera. He persuaded the dean of the physics department at the University of Minnesota to allocate $ 7,000 to repair it and installed equipment to analyze the records in his home.
The unique footage of the giant discharges frightened Winkler as much as it made him happy. What if such a discharge hits the aircraft? And the scientist turned to his colleagues from NASA with a warning. They began to doubt. What are the discharges? But out of deference to Winkler's past, they took a look at the recordings of the space shuttle flights. And they could not believe their eyes: more than a dozen of such discharges were found on the films. Winkler got it right. As a professional, he brought the matter to its logical conclusion - publications in the leading scientific journals Geophysical Research Letters (1989) and Science (1990).
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The articles literally shocked specialists in astronomy, atmospheric electricity, radiophysics, atmospheric acoustics, gas discharge physics and aerospace security. After these publications, NASA could no longer shrug off the possible threat to spacecraft and began a detailed study of high-altitude discharges. During the three years of preparation for this work, Winkler was repeatedly consulted, but was never included in the program itself.
On the very first night of observations, July 7, 1993, at a scientific station near Fort Collins (Colorado), surprised researchers recorded more than 240 high-altitude discharges. The next night, a dedicated flying laboratory aboard the DC-8 aircraft was deployed to rule out an error in the determination of altitude. The results exceeded all expectations: huge flares were detected at altitudes of at least 50-60 kilometers. In honor of the restless Pak from Shakespeare's "A Midsummer Night's Dream" they were given the name sprites, that is, air spirits. Naturally, the question arose: why did they not know about these discharges before, if each powerful thunderstorm front generates dozens of them?
Analysis of the literature has shown that over hundreds of years many people have seen unusual and very large discharges above the clouds. They were called rocket lightning, cloudy stratospheric discharges, ascending lightning and even cloud-to-space lightning. But in the absence of reliable evidence, strange eyewitness reports were simply ignored. They even brushed aside such a well-known and honored specialist in the field of atmospheric electricity as the Nobel laureate Charles Thomson Wilson, who wrote about a similar phenomenon in his article back in 1956. It took the flair, experience, perseverance and fearlessness of Professor John Winkler, so that "this cannot be" very quickly turned into "but who does not know this." Now, on numerous videos on the Internet, you can examine these categories in detail.
John Winkler died in 2001. He did not do more work on high-altitude grades, although it is hard to believe that he did not want to - after such and such success. His publication in Science was regularly referred to, but apparently not included in the projects. The obituary written by his colleagues shows resentment for him. But in vain. Red and purple sprites are saluted to John Randolph Winkler every day because he taught people to see them.
Soon, researchers discovered a whole light show unfolding in the upper atmosphere above the lead thunderstorms. The main actors in it (in order from bottom to top): blue jets, which are sometimes called gnomes (since they are at the bottom), in the middle are red-purple sprites and halos, and above them are reddish rings - elves hovering in the height. But, of course, we must not forget the director behind the grandiose performance - these are the well-known storm clouds and lightning. Actually, until recently, the troupe was more numerous, but the researchers gradually got rid of spirits, jellyfish (some types of sprites) and other sonorous "living creatures".
It should be noted that exercises in beautiful names are not just fun in the style of "physics joking", as it might seem at first glance. As in show business, in science the promotion of ideas and trends plays an important role, because here and there there is a struggle for resources. The field of science that is heard by the public is usually more generously funded. Remember at least nanotechnology, which everyone is talking about, but no one can really explain what it is and why so much money needs to be directed there. But let us return to our performance and introduce everyone in more detail to the most respectable audience.
Elves are the most ephemeral and short-lived in the high-altitude family. These glowing red-violet rings appear in the lower ionosphere at altitudes of 80-100 kilometers. In less than a millisecond, the glow, appearing in the center, expands to 300-400 kilometers and fades away. The elves have not been studied in great detail, probably because they do not cause much controversy and do not promise serious progress in understanding the nature of atmospheric discharges. They are born three ten-thousandths of a second (300 microseconds) after a strong lightning strikes from a thundercloud into the ground. Its trunk becomes a "transmitting antenna", from which a powerful spherical electromagnetic wave of very low frequency starts at the speed of light. In 300 microseconds, it just gets to an altitude of 100 kilometers, where it excites the red-violet glow of nitrogen molecules. The further the wave goesthe wider the ring becomes, until it fades away from the source.
Blue jets, or gnomes, are the most mysterious, rare and difficult to observe creatures in the ensemble of new high-altitude discharges. The gnome looks like a blue narrow inverted cone, starting from the upper edge of a thundercloud and sometimes reaching 40 kilometers in height. The propagation speed of blue jets is from 10 to 100 km / s. But the strangest thing is that their appearance is not always associated with visible lightning strikes. At the altitudes from which the jets are launched, the pressure is still relatively high, and it is not surprising that they are blue. This is how lightning, corona discharge on wires, spark discharge and even high temperature flames shine. This is also the glow of nitrogen molecules, but not in the red-violet stripe, as in the case of elves, but in ultraviolet-blue.
In addition to ordinary jets, so-called blue starters sometimes break up from the upper edge of the cloud. They do not rise above 30 kilometers. Some scientists believe that this is just a lightning bolt directed upward into an area where the pressure drops rapidly, and therefore starters expand much more than conventional lightning. Others consider them to be underdeveloped jets.
But the most interesting type of blue jets has been called giant jets. Starting not very far from the surface of the Earth, they reach 90 kilometers in height. The interest of geophysicists in giant jets to match their size, because these discharges make a "non-stop flight" from the troposphere directly to the ionosphere. However, they are extremely rare, and have been reliably recorded no more than a dozen times. At the same time, they live for a fraction of a second, which, in principle, allows them to be noticed with the naked eye.
Jet theory is only making its first steps. It is not even clear yet what this phenomenon looks like. If by their nature they are close to the luminous channel of lightning in the development stage, then it becomes clear why the birth of a jet is not associated with lightning: it itself is lightning. But, perhaps, a closer analogy is the discharge inside a thundercloud, which energizes the lightning channel. In this case, it will be even more difficult to understand the nature of the jets, since the theory of such discharges is at an early stage of development.
The largest number of observations and publications is devoted to red sprites. These are real pop stars among high-altitude atmospheric discharges. Sometimes it seems that interest in them is just as overheated as in popular singers. Why did they deserve such attention? The point is probably that they are easy to observe (if, of course, you know that it is possible). Tens of thousands of sprites are born on the globe every day, and it's amazing that they haven't been noticed for so long.
Sprites are very bright volumetric flares that occur at an altitude of 70-90 kilometers and descend 30-40 kilometers, and sometimes more. In the upper part, their width sometimes reaches tens of kilometers. These are the most voluminous of the high-altitude discharges. Like elves, sprites are closely related to lightning, but not all. Most lightning strikes from the negatively charged part of the cloud (on average, it is closer to the ground). But 10% of lightning striking the ground start from the area of a positive charge, and since the main area of the location of the positive charge is greater than that of the negative one, then positive lightning is more powerful. It is believed that such powerful discharges generate sprites that flash in the mesosphere about a hundredth of a second after a cloud-to-earth discharge.
The red-purple color of sprites, like that of elves, is associated with atmospheric nitrogen. The upper part of the sprite glows uniformly, but below 70 kilometers, the discharge seems to be woven from channels hundreds of meters thick. Their structure is the most interesting feature of sprites to study. Channels are called streamers by analogy with the well-known needle discharges at sharp edges of objects in thunderstorms and at high-voltage wires. True, the thickness of terrestrial streamers is on the order of a millimeter, and in sprites they are 100,000 times larger. It is not yet clear why the diameter of streamers increases so much - much faster than the air pressure decreases with height.
The halo is a uniform reddish-purple glow at an altitude of about 80 kilometers. The reason for the discharge is apparently the same as for the top of the sprites, but unlike them, the halo always appears directly above the lightning flash. Sprites take the liberty of being somewhere on the side. There seems to be some connection between sprites and halos, but the mechanism is still unclear. They appear sometimes together, sometimes separately. Perhaps the halo is the upper part of the sprites, when the electric field strength was not enough for the discharge to spread into the denser lower air.
According to the Geographic Map of Thunderstorms, residents of the equatorial and tropical zones of the Earth have the greatest chances of seeing sprites. It is in this area that up to 78% of all thunderstorms occur. Residents of Russia can also observe sprites. The peak of thunderstorms in our country falls on July-August. It was at this time that astronomy lovers can see such a beautiful phenomenon as sprites.
According to the American Sprite and Giant Jet Observing Handbook, in order to see the sprites, the observer must be approximately 100 kilometers from the epicenter of the storm. In order to observe the jets, he should aim his optics at 30-35 degrees towards the thunderstorm area. Then he will be able to observe a part of the ionosphere at an altitude of 50 kilometers, it is in this area that jets appear most often. To observe the sprites, you should aim the binoculars at an angle of 45-50 degrees, which will correspond to the area of the sky at an altitude of about 80 km - the place where sprites are born.
For a better and more detailed study of sprites, jets, and even more elves, it is better for the observer to use special cinema equipment, which will allow to record in detail the heavenly flares. The best time to hunt for sprites in Russia is from mid-July to mid-August.
Sprites, like lightning, are found not only on Earth, but also on other planets of the solar system. Presumably, it was the sprites that were recorded by space research vehicles during severe storms on Venus, Saturn and Jupiter.
Sprites and elves appear at such high altitudes due to the strong ionization of the air by galactic dust. At an altitude of over 80 kilometers, the conductivity of current is ten billion times higher than in the surface layers of the atmosphere.
The name "sprites" comes from the name of the forest spirits, which are referred to in William Shakespeare's comedy "A Midsummer Night's Dream."
Sprites were known to mankind long before 1989. People have expressed various hypotheses about the nature of this phenomenon, including the fact that flashes of light are alien spaceships. It was only after John Winkler was able to capture frames of sprites in the ionosphere that scientists proved that they are of electrical origin.
The color of sprites, jets, and elves differs depending on the height at which they appear. The fact is that more air is concentrated in the near-Earth atmosphere, while a high concentration of nitrogen is observed in the upper layers of the ionosphere. Air burns with blue and white flame, nitrogen - red. For this reason, the jets below the sprites are predominantly blue, while the sprites themselves and, higher, elves, are reddish.
And here is a video of a very rare phenomenon - rising lightning:
