Fleeting “spirits”: Russian physicists are closer to unraveling the mysterious phenomenon

Real high-altitude flare hunters – “spirits of the air” (or sprites) from the Institute of Applied Physics of the Russian Academy of Sciences recreated the object of their study in the laboratory. In a small vacuum chamber, they caught a fleeting “spirit” that existed for hundredths of a second, similar to those that usually occur at altitudes above 50 kilometers above the Earth, above thunderclouds. About what other “essences” can appear in the sky, why they need to be investigated, we talked with the author of the project, Candidate of Physical and Mathematical Sciences Andrei Yevtushenko.

Even 30 years ago, someone who described such phenomena could be called an eccentric, because few people believed in the existence of “sprites” (from the Latin spiritus – “spirit”), elves and other atmospheric fairy-tale characters. There are two reasons why strange high-altitude flares have managed to hide from scientists for a long time. Firstly, they are almost impossible to see with the naked eye, because they are very short-lived, that is, they occur in 10-15 milliseconds, which is more fleeting than the change of the 25th frame. Secondly, they flare up only on the other side of the clouds, and in order to fix them with the help of the highest-speed camera, one must also find a convenient position, for example, by chance to be on an airplane flying above the clouds. Thirdly, modern video cameras capable of “catching” these amazing flashes have appeared relatively recently.

The first to discover high-altitude flares was Professor John Randolph Winkler, a 73-year-old NASA veteran. It happened in 1989. The scientist pointed a video camera at thunderclouds, and then, looking through the film frame by frame, he discovered bright flashes that, unlike ordinary lightning, occurred above the clouds. The “show” took place between 14 and 40 kilometers above the Earth’s surface.

After Winkler’s discovery was confirmed by other researchers, a boom in research in this area began. It soon became clear that there were many “inhabitants” of the back side of the clouds: they were classified (as their height and shape increased) into jets, sprites, halos and elves.

– Andrey Alexandrovich, let’s first deal with all these phenomena, how do they differ from each other?

Let’s start with those that arise below all the others. These are jets (from the English “jet” – jet) – high-altitude flashes, which are also called reverse lightning, which are discharged from the clouds not towards the earth, but towards the sky. Jets are characterized by a blue color (it depends on the density of the atmosphere at those altitudes where flashes occur). Jets are divided into blue starters, which “shoot” up to 20-25 kilometers up, into classic jets, which reach 50 kilometers, and giant jets, which can stretch up to 90 km). At altitudes from 50 to 90 km, sprites appear that already have red or pink colors. These flashes directly depend on the parent ordinary lightning (they are, as it were, its echo from the back of a thundercloud). They are also different. For the outward resemblance of some to jellyfish, whose “tentacles” are directed to the ground, they are called so – “jellyfish sprite”. Others are more like a carrot in shape – “carrot sprite”. There is also a halo – a diffuse, diffuse glow that forms instead of a sprite. And finally, the elves. They also occur at high altitudes of about 85-90 km, are red in color and represent the reaction of the atmosphere to an electromagnetic pulse coming from a conventional lightning discharge. Notice the “elf” is even more difficult than jets and sprites – it occurs, on average, for one millisecond. But thanks to the high-speed cameras that filmed them, we know that this is a radially diverging ring at altitudes of about 90 km, a kind of expanding luminous steering wheel.

– Why did you choose sprites as the object of your research?

– They occur more often than other phenomena. In addition, our work on the development of the sprite map and their modeling did not start from scratch – before that, we investigated ordinary lightning and currents that occur in the atmosphere. And sprites are directly dependent on them (which cannot be said about jets that are born on their own).

– Tell us about sprite modeling in the laboratory. How did you do it?

– We built a vacuum chamber with a volume of 4 cubic meters, installed two electrodes in it to bring the potential and created a pressure close to what occurs in the mesosphere, where natural sprites are born (it is several thousand times less than that in in which we live). But the subtlety is that in nature the pressure in different areas of the discharge propagation is different. That is why sprites take the form of either jellyfish or carrots. And in order to achieve similarity, we also set a goal for ourselves: to create pressure drops in our installation.

– And what sprite did you end up with?

Ours looked more like a carrot.

– Where in nature can you find more sprites?

– Various high-altitude flashes are more common in the tropics and subtropics, where the most active convection events occur (active vertical heat transfer in the atmosphere – Auth.). These are the Caribbean, Southeast Asia, Africa, the Mediterranean.

– Is it impossible to fix a sprite in Russia?

– Sometimes they are found in our latitudes. One of my colleagues once took a photo of a sprite from Moscow. True, the cloud over which it arose was at that moment approximately over Tver.

– How is it possible – to fix the flash at such a distance ?!

– Such events are the only way to “catch”. To catch a sprite (or jet), you need to be where there is no thunderstorm and a clear sky above your head. You need to look where powerful thunderstorm activity is observed at a distance of about 100-200 km. Then there will be high chances for a high-sensitivity camera to capture a sprite.