Sprites or red sprites are large-scale electric discharges that occur in the mesosphere, high above thunderstorm clouds, or cumulonimbus, giving rise to a varied range of visual shapes flickering in the night sky. They are usually triggered by the discharges of positive lightning between an underlying thundercloud and the ground.

First color image of a sprite, taken from an aircraft
A sprite over Laos, as seen from the ISS

Sprites appear as luminous red-orange flashes. They often occur in clusters above the troposphere at an altitude range of 50–90 km (31–56 mi). Sporadic visual reports of sprites go back at least to 1886.[1] They were first photographed on July 4, 1989,[2] by scientists from the University of Minnesota and have subsequently been captured in video recordings thousands of times.

Sprites are sometimes inaccurately called upper-atmospheric lightning. However, they are cold plasma phenomena that lack the hot channel temperatures of tropospheric lightning, so they are more akin to fluorescent tube discharges than to lightning discharges. Sprites are associated with various other upper-atmospheric optical phenomena including blue jets and ELVES.[1]

History edit

The earliest known report is by Toynbee and Mackenzie in 1886.[3] Nobel laureate C. T. R. Wilson had suggested in 1925, on theoretical grounds, that electrical breakdown could occur in the upper atmosphere, and in 1956 he witnessed what possibly could have been a sprite. They were first documented photographically on July 6, 1989, when scientists from the University of Minnesota, using a low-light video camera, accidentally captured the first image of what would subsequently become known as a sprite.[4]

Several years after their discovery they were named sprites (air spirits) after their elusive nature.[5] Since the 1989 video capture, sprites have been imaged from the ground, from aircraft and from space, and have become the subject of intensive investigations. A featured high speed video that was captured by Thomas Ashcraft, Jacob L Harley, Matthew G McHarg, and Hans Nielsen in 2019 at about 100,000 frames per second is fast enough to provide better detailing of how sprites develop. However, according to NASA's APOD blog, despite being recorded in photographs and videos for the more than 30 years, the "root cause" of sprite lightning remains unknown, "apart from a general association with positive cloud-to-ground lightning." NASA also notes that not all storms exhibit sprite lightning.[6]

In 2016, sprites were observed during Hurricane Matthew's passage through the Caribbean.[7] The role of sprites in the tropical cyclones is presently unknown.[8]

Characteristics edit

Different types of electrical phenomena in the atmosphere
A sprite seen from the International Space Station (top right, faint red above the lightning).
ISS sprite image above; zoomed in
Another shot from the first color clip of the sprite.

Sprites have been observed over North America,[9] Central America, South America,[10] Europe,[11] Central Africa (Zaire), Australia, the Sea of Japan and Asia and are believed to occur during most large thunderstorm systems.

Rodger (1999) categorized three types of sprites based on their visual appearance.[1]

  • Jellyfish sprite – very large, up to 50 by 50 km (31 by 31 mi).
  • Column sprite (C-sprite) – large scale electrical discharges above the earth that are still not totally understood.
  • Carrot sprite – a column sprite with long tendrils.

Sprites are colored reddish-orange[5] in their upper regions, with bluish hanging tendrils below, and can be preceded by a reddish halo. They last longer than normal lower stratospheric discharges, which last typically a few milliseconds, and are usually triggered by the discharges of positive lightning between the thundercloud and the ground,[12] although sprites generated by negative ground flashes have also been observed.[13] They often occur in clusters of two or more, and typically span the altitude range 50 to 90 kilometres (31 to 56 mi), with what appear to be tendrils hanging below, and branches reaching above.[5]

Optical imaging using a 10,000 frame-per-second high speed camera showed that sprites are actually clusters of small, decameter scale, (10–100 m or 33–328 ft) balls of ionization that are launched at an altitude of about 80 km (50 mi) and then move downward at speeds of up to ten percent the speed of light, followed a few milliseconds later by a separate set of upward moving balls of ionization.[14] Sprites may be horizontally displaced by 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 on rare occasions may be up to 100 milliseconds.

This footage from the ISS shows a red sprite over East Asia immediately before 0:07, directly above the large lightning flash towards the upper right of the frame.

In order to film sprites from Earth, special conditions must be present: 150–500 km (93–311 mi) of clear view to a powerful thunderstorm with positive lightning between cloud and ground, red-sensitive recording equipment, and a black unlit sky.[15]

Sprite halo edit

Sprites are sometimes preceded, by about 1 millisecond, by a sprite halo, a pancake-shaped region of weak, transient optical emissions approximately 50 kilometres (31 mi) across and 10 kilometres (6.2 mi) thick. The halo is centered at about 70 kilometres (43 mi) altitude above the initiating lightning strike. These halos are thought to be produced by the same physical process that produces sprites, but for which the ionization is too weak to cross the threshold required for streamer formation. They are sometimes mistaken for ELVES, due to their visual similarity and short duration.[16][17][18]

Research carried out at Stanford University in 2000 indicates that, unlike sprites with bright vertical columnar structure, occurrence of sprite halos is not unusual in association with normal (negative) lightning discharges.[18] Research in 2004 by scientists from Tohoku University found that very low frequency emissions occur at the same time as the sprite, indicating that a discharge within the cloud may generate the sprites.[19]

Related aircraft damage edit

Sprites have been blamed for otherwise unexplained accidents involving high altitude vehicular operations above thunderstorms. One example of this is the malfunction of a 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. Months after the accident, an investigation concluded that a "bolt of lightning" traveling upward from the clouds provoked the incident.[20] The attribution of the accident to a sprite was made retroactively, since this term was not coined until late 1993.

See also edit

References edit

  1. ^ a b c Rodger, C. J. (1999). "Red sprites, upward lightning, and VLF perturbations". Reviews of Geophysics. 37 (3): 317–336. doi:10.1029/2001JA000283.
  2. ^ "NASA - Heliophysics Nugget: Seeing Sprites".
  3. ^ Toynbee, Henry (14 January 1886). "Meteorological phenomena (letter)". Nature. 33 (846): 245. doi:10.1038/033245d0. S2CID 4128139.
  4. ^ Franz, R.C.; Nemzek, R.J.; Winckler, J.R. (1990). "Television Image of a Large Upward Electrical Discharge Above a Thunderstorm System". Science. 249 (4964): 48–51. Bibcode:1990Sci...249...48F. doi:10.1126/science.249.4964.48. PMID 17787625. S2CID 9343018.
  5. ^ a b c Sentman, D.D.; Wescott, E. M.; Osborne, D. L.; Hampton, D. L.; Heavner, M. J. (1995). "Preliminary results from the Sprites94 aircraft campaign: 1. Red Sprites". Geophys. Res. Lett. 22 (10): 1205–1208. Bibcode:1995GeoRL..22.1205S. doi:10.1029/95GL00583.
  6. ^ "Sprite Lightning at 100,000 Frames Per Second". APOD.NASA.gov. NASA's APOD (Astronomy Picture of the Day blog). Retrieved 19 July 2022.
  7. ^ "Rare, Colorful Lightning Sprites Dance Over Hurricane Matthew". National Geographic. October 3, 2016. Archived from the original on October 4, 2016. Retrieved October 3, 2016.
  8. ^ "Hurricane Matthew and the Day/Night Band". Cooperative Institute for Meteorological Satellite Studies. University of Wisconsin–Madison. October 7, 2016. Retrieved November 3, 2016.
  9. ^ Kathy Berry (1994). Spectacular Color Flashes Recorded Above Electrical Storms. NASA. Retrieved on 2009-02-18.
  10. ^ Don Savage and Kathy Berry (1995). Sprites Confirmed Over Storms Outside U.S. For First Time. NASA. Retrieved on 2009-02-18.
  11. ^ "Rare Atmospheric Phenomenon Observed from Armagh". Archived from the original on 2013-09-05. Retrieved 2013-08-21.
  12. ^ Boccippio, D. J.; Williams, ER; Heckman, SJ; Lyons, WA; Baker, IT; Boldi, R (August 1995). "Sprites, ELF Transients, and Positive Ground Strokes". Science. 269 (5227): 1088–1091. Bibcode:1995Sci...269.1088B. doi:10.1126/science.269.5227.1088. PMID 17755531. S2CID 8840716.
  13. ^ Lu, Gaopeng; Cummer, Steven A; Blakeslee, Richard J; Weiss, Stephanie; Beasley, William H (2012). "Lightning morphology and impulse charge moment change of high peak current negative strokes". Journal of Geophysical Research: Atmospheres. 117 (D4): n/a. Bibcode:2012JGRD..117.4212L. CiteSeerX doi:10.1029/2011JD016890.
  14. ^ Stenbaek-Nielsen, H. C.; McHarg, M.G.; Kanmae, T.; Sentman, D.D. (June 6, 2007). "Observed emission rates in sprite streamer heads". Geophys. Res. Lett. 34 (11): L11105. Bibcode:2007GeoRL..3411105S. doi:10.1029/2007GL029881. L11105.
  15. ^ Grønne, Jesper. "Første danske 'red sprites' fanget fra Silkeborg" Archived August 22, 2012, at the Wayback Machine Danish Meteorological Institute, 20 August 2012. Retrieved: 20 August 2012.
  16. ^ Rina Miyasato, Hiroshi Fukunishi, Yukihiro Takahashi, Michael J. Taylor, Hans. C. Stenbaek-Nielsen (2002). Characteristics of Lightning-induced Sprite Halos and Their Generation Mechanisms. Academic Society Home Village. Retrieved on 2009-02-18.[dead link]
  17. ^ Christopher Barrington Leigh (2000). Sprite halos. Archived 2008-09-17 at the Wayback Machine Stanford University. Retrieved on 2008-02-18.
  18. ^ a b Barrington-Leigh, C. P., U. S. Inan, and M. Stanley, "Identification of Sprites and Elves with Intensified Video and Broadband Array Photometry", J. Geophys. Res. 106, No. 2, February, 2001.
  19. ^ Ohkubo, A.; Fukunishi, H.; Takahashi, Y.; Adachi, T. (2005). "VLF/ELF sferic evidence for in-cloud discharge activity producing sprites". Geophysical Research Letters. 32 (4): L04812. Bibcode:2005GeoRL..32.4812O. doi:10.1029/2004GL021943. S2CID 53059204.
  20. ^ STRATOCAT (2009). "Data of the stratospheric balloon launched on 6/5/1989 from Columbia Scientific Balloon Facility, Palestine, Texas, US for Molecules observation made fluorescent with a Laser". Retrieved 2009-02-18.

External links edit