Sprites, blue jets, gigantic jets, elves – Upper Atmosphere Lightning
If ordinary lightning seems pretty ordinary, upper atmosphere lightning is something else – an entire ZOO of various types of upper atmosphere electrical discharges.
There is anecdotal evidence of sightings of upper atmosphere lightning, or Transient Luminous Events (TLEs), at least as far back as the 1730s, while proper visual reports of sightings go back to 1886. It was confirmed, photographically, on July 6, 1989, by scientists of the University of Minnesota. Using low light digital cameras, upper atmosphere is now routinely detected and recorded at increasingly high resolutions.
Many types of Transient Luminous Events
There are many types of Transient Luminous Events. The most common and well known are sprites, but there is a number of 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 Preturbations Resulting from Intense Thunderstorm Electrification. They are reddish-orange in color. Unlike tropospheric lightning, sprites are cold plasma, similar to fluorescent tube discharge. Based on their shape and visual appearance, we distinguish three types of sprites: 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 in color. They are not connected to lightning strikes. A smaller variation of blue jets are blue starters, which are 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, similar 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 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.
Seeing Transient Luminous Events – with your own eyes
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 really 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. Often the parent storm is so far that it is below the horizon, so 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. Structure can be seen with the brightest sprites. 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 blue starters can also be seen sometimes, generally when the storm is closer and in sight (due to their lower peak altitudes). Visual sightings of blue jets and starters are very rare.
Photographing Transient Luminous Events – with your own camera
Got a DSLR or mirrorless camera? You can try to capture sprites on photos. Again, 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 make many photos before capturing a sprite!