Sprite (Lightning)

Upper atmospheric phenomena powered by thunderstorms, including terrestrial Gamma Ray Flashes and Transient Luminous Emissions (TLEs), electrical discharges that include blue glimpses at the top of thunderstorms, blue jet, gigantic jet, red sprite, haloes, and elves.
Credits: DTU Space, TGF: NASA
Source: https://www.nasa.gov/mission_pages/station/research/Once_Upon_a_Time_in_a_Thunderstorm

The phenomenon which occurs in the sky over our heads, not the sea is the lightning known as a red sprite. This lightning is rarely photographed in this detail. Sprites have been recorded for over 30 years, but their root cause remains unknown. These mysterious bursts of light in the upper atmosphere resemble for a very short period of time gigantic jellyfish. A high-speed video was been taken a few years ago detailing how red sprites actually develop. The featured image was captured in high definition from Italy. Sprites are relatively very cold, they operate long vividly colorful light tubes then hot compact light bulbs. The luminous flashes only take a fraction of a second to occur and can be seen in the best way when very powerful thunderstorms are visible. 

The large-scale electrical discharges

A scientist from the University of Minnesota had first photographed red sprites on July 6, 1989, and afterward, it has been captured in audio and recording several times.

The sprites appear as radiant reddish-orange flashes which frequently occur in congregate above the atmosphere at a 50-90km (31-56mi) range of altitude. Sometimes inexactly Sprites are also called upper-atmospheric lightning. Sprites are cold plasma occurrence that lacks the hot channel temperatures of tropospheric lightning, sprites are more equivalent to fluorescent tube discharges than to lightning discharges.

Red sprites are scaped as jellyfish steaks in the sky which are considered to be rare phenomena or evasive to human eyes. Dr. Davis Sentman from the University of Alaska was the first man who proposed the name “sprite” and used it in literature by W.A. Lyons in 1994.

Let’s explore the evolution of Red Sprite:

The transient optical above the thunderclouds are earlier known report from Johann Georg Estor in 1730 and another report in 1886 by Toynbee and Mackenzie.

Nobel laureate C.T.R Wilson suggested in 1925 on theoretical grounds, that electronic breakdowns occur in the upper atmosphere. In 1956, C.T.R Wilson witnessed what more possibly could have been a sprite. Scientists from the University of Minnesota were the first to document it photographically with a low-light video camera and accidentally captured the very first image of large-scale electrical discharge which later on become to be known as a Sprite.

After several years of research and discovery, they have named sprites (air sprites). Sprites have been imaged from the ground since the video have been captured in 1989, and from space and aircraft it has become the subject of intensive investigations.

During Hurricane Matthew’s passage through the Caribbean in 2026, sprites were observed. But presently the role of sprites is unknown in tropical cyclones.

Classes of Sprites based on their visual appearance:

Countries from where Sprites have been observed – North America, Central America, Europe, South America, Sea of Japan, and in some Asian parts, and are believed to occur during most large thunderstorm system.

  • Carrot Sprite – This sprit is long ringlets with columns and reddish-orange colored in their upper regions. This sprite often occurs in congregate of two or more and stretches the altitude range 50 to 90 kilometers (31 to 56 mi). It is also been observed that sprites are generated by negative ground flashes. This sprite lasts longer than the normal lower stratospheric discharges and lasts for few milliseconds. The sprites are triggered by the discharges of positive lightning between the ground and thundercloud. 
  • Column Sprite (C-sprite) – This sprite is the large electrical discharges above the earth that are still not understood.
  • Jellyfish Sprite – These are very large, up to 50 by 50 km (31 by 31 mi).

To shoot a film of the sprite from the earth, a special condition must be taken as like a clear view of 150-500 km (93-311 mi) powered thunderstorm with positive lightning between ground and cloud, the sky should be dusky black and red-sensitive recording equipment.

Sprites are the small ionize clustered balls of diameter-sized (10-100 m or 33-328 ft) launched at an altitude of about 80km (50 mi) and moves downward at speed of up to 10 percent the speed of light. The sprites are displayed horizontally up to 50 km (31 mi) from the location of the underlying lightning strike, with a time delay following the lightning that is typically a few milliseconds, but it may be up to 100 milliseconds on rare occasions.

Causes of large-scale electrical discharges:

  1. Model 1: Quasi-Electrostatic Field – The cloud charges up before the lightning discharge including a negative shielding layer. The positive CG removes the positive charge but the negative shielding layer remains over a much longer time scale. The negative shielding layer remains after the discharge causing polarization in the atmosphere and a quasi-static E-field. This strong E-field causes electrical breakdown producing sprites.
  2. Model 2: Runaway Electron Breakdown – High energy electrons produced by cosmic rays are accelerated by the quasi-static electric field. Through collisions, these electrons produce ions and new electrons. Most of these new electrons thermalize due to collisions, but some accelerate in the electric field allowing runaway breakdown. Since below 1MeV, the stopping power decreases with increasing electron energy, the higher electrons can accelerate rather than thermalize.

In this sufficiently strong electric field, these accelerating electrons produce an avalanche effect that allows the number of electrons to grow exponentially, known as runaway breakdown.

  • Model 3: Electromagnetic Pulse – The electromagnetic pulse from the return stroke of large lightning strikes causes an electrical breakdown of the high altitude atmosphere above the thunderstorm (Rowland et al., 1995; Valdiva et al., 1997). Since the charge is transferred very quickly (o.1ms) during the return stroke, the EMP is a radiation and inductive field phenomenon. Since sprites occur at least 5ms after the positive CG, the EMP model seems to better explain another related phenomenon known as Elves which occurs 0.35ms after the positive CG.

Do you know what is Sprite halo?

Sprites halos were mistaken as elves until 1999. This is the optical phenomena of the upper atmosphere associated with thunderstorms, and are disable disk-shaped glows that anticipate sprites and propagate downward.

The Sprite Halo was first observed from Wyoming Infrared Observatory on July 28, 1998, 5:06:26.303. Sometimes sprites pave the way by about 1 millisecond, by sprite halo, a pancake-shaped region of weak, transient optical emissions approximately 50 kilometers (31 mi) across and 10 kilometers (6.2 mi) thick.

The halos are thought to be produced sprites, but for which the ionization is too weak to cross the threshold required for streamer formation. The hole is centered at about 70 kilometers (43mi) altitude above the initiating lightning strike.

At Stanford University in 2000, the research carried out indicates that unalike sprites the bright vertical columnar structure, occurrence of sprite halos is not unusual in association with normal (negative) lightning discharges. The research of 2004 by Tohoku University scientists found that very low-frequency emissions occur at the same time as the sprite, indicting that a discharge within the cloud may generate the sprites.

Properties of Sprite:

  • Sprites are associated with positive cloud-to-ground (CG) lightning, and they last from about 5ms to 300ms (Rodger, 1999).
  • Sprites usually have a column-like composition, with a lot of fine structure.
  • They extend from about 30-40km to about 70-90km, with a primary body at about 50-60km.
  • Their horizontal extent is about 50-60km.
  • The main upper portion of a sprite is red color, while the lower tendrils go from red to blue with decreasing altitude (stuntman et al, 1995).
  • Sprites are directly correlated with positive CG strokes from large thunderclouds.
  • Only 10% of all lightning is positive CG.

Aircraft Damage caused by Sprite:

Sprites have been blamed for the accidents involving high altitude vehicular operations above thunderstorms. For example, the malfunction of NASA stratospheric balloon launched on June 6, 1989, from Palestine Texas. The balloon suffered an uncommanded payload release while flying at 120,000 feet (37,000 m) over a thunderstorm near Graham, Texas. After some months of an accident. An investigation concluded that a “bolt of lightning” traveling upward from the clouds provoked the incident. The ascription of the accident to sprite has made it retrospective since this term was coined until late 1993.

Sources:

https://en.m.wikipedia.org/wiki/Sprite_(lightning)

https://science.nasa.gov/sprite-lightning-hd

What are lightning sprites?

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