If ordinary lightning seems pretty ordinary, upper-atmosphere lightning is something else – an entire zoo of various upper-atmosphere electrical discharges. Red sprites, gigantic and blue jets, to name a few.
There is anecdotal evidence of lightning sightings in the upper atmosphere, or Transient Luminous Events (TLEs), at least as far back as the 1730s. In contrast, proper visual reports of sightings go back to 1886. It was confirmed photographically on July 6, 1989, by scientists at the University of Minnesota.
Low-light digital cameras routinely detect and record the upper atmosphere at increasingly high resolutions.
Types of Transient Luminous Events (TLEs)
There are many types of Transient Luminous Events. The most common and well-known are sprites, but there are several other types, too:
- Sprites: reach 50 – 90 km in altitude and are triggered by positive CG lightning. Sprite is also an acronym for Stratospheric/mesospheric Perturbations Resulting from Intense Thunderstorm Electrification. They are reddish-orange. Unlike tropospheric lightning, sprites are cold plasma, similar to fluorescent tube discharge. We distinguish three sprites based on their shape and visual appearance: jellyfish, column, and carrot sprites.
- Blue jets: project directly from the top of the thunderstorm in a narrow cone jet up to approximately 50 km altitude. Unlike sprites, blue jets are, as the name implies, blue. They are not connected to lightning strikes. A minor variation of blue jets are blue starters, similar to blue jets, but only reach about 20 km high up and are thought to be ‘failed’ blue jets.
- Gigantic jets are similar to blue jets but reach 70 km high and are exceedingly rare. The upper parts of gigantic jets produce red emissions, identical to sprites. Only a handful have been photographed or captured on video.
- Other sprite halos and elves are rare and indistinct types of TLEs, producing large diffuse glows in the case of elves up to 400 km in diameter
Sprite photographed from the International Space Station above a thunderstorm over NW Mexico on August 10, 2015. Photo: NASA Earth Observatory.
Observing Red sprites or Gigantic jets
You can actually *see* Transient Luminous Events. Sprites are by far the most frequent, and they are the most likely to be seen. Under a dark sky – rural skies far from light pollution or high in the mountains, also far from light pollution – they can be seen as brief flashes above distant thunderstorms.
The parent storm is often so far that it is below the horizon that only sprites appear. As a rule of thumb, the sky is dark enough to see sprites if you can clearly and distinctly see the Milky Way close to the horizon. Otherwise, your chances of spotting a sprite are low. The structure can be seen with the brightest sprites.
Gigantic Jets over Himalayan Mountains; photo by Li Xuanhua
Remember that sprites appear high above their parent storms: they can reach halfway up (45°) in the sky if the parent storm is 50-100 km away and will occur low near the horizon for thunderstorms hundreds of kilometers away.
Blue jets and starters can sometimes be seen when the storm is closer and inclined (due to their lower peak altitudes).
Visual sightings of blue jets and starters are infrequent.
Photographing TLEs with your camera
You can try to capture sprites on photos with DSLR or mirrorless camera. You will need dark skies.
Set your camera on a tripod, set the ISO to high values (3200 or more), and exposures several seconds long. Use a ‘fast’ lens, f/1.8 or f/1.4 (or faster if possible) – a 50 mm lens will do fine. Be prepared to take many photos before capturing a sprite!
Red sprites over Slovenia, photo by Marko Korosec
Below are a few examples of red sprites, gigantic jets, blue jets, and elves:
SPRITES
GIGANTIC JETS
BLUE JETS
ELVES
See also: