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Subauroral ion drift

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Atmospheric phenomenon

A subauroral ion drift (SAID), also known as a polarisation jet, is an atmospheric phenomenon driven by substorms in the Earth's magnetosphere. First discovered in 1971, a SAID is a latitudinally narrow (1-2° MLAT) layer of rapid, westward flowing ions in the Earth’s ionosphere. Though not traditionally associated with an optical emission, the STEVE discovery paper suggested the first link between this optical emission’s occurrence and that of an extremely fast and hot SAID event.

SAIDs are observed equatorward of the auroral zone, at subauroral latitudes, typically in the local time sector between 18:00 hours and 22:00 hours. They can occur individually, or as multiple events. SAIDs are characterised by a reduced density of ions, a strong westward flow, and an increased temperature. They can last between 30 minutes and 3 hours. The exact characteristics of SAID events appear to have solar cycle, seasonal, and diurnal dependences.

Although studied for decades, prior to the formal discovery of STEVE, SAIDs had never been associated with an optical emission. STEVE was associated with a particularly extreme SAID, with a velocity over twice the norm and 100 K hotter. STEVE has presented a new way for scientists, including citizen scientists, to study SAIDs.

References

  1. ^ Spiro, R. W.; Heelis, R. A.; Hanson, W. B. (August 1979). "Rapid subauroral ion drifts observed by Atmosphere Explorer C". Geophysical Research Letters. 6 (8): 657–660. Bibcode:1979GeoRL...6..657S. doi:10.1029/GL006i008p00657.
  2. Galperin, Y. I.; Ponomarov, Y. N.; Zosinova, A. G. (1973). "Direct measurements of ion drift velocity in the upper ionosphere during a magnetic storm". Cosmicheskie Issled. 11: 273. Bibcode:1973KosIs..11..273G.
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  4. Patel, Kasha (14 March 2018). "Mystery of Purple Lights in Sky Solved With Citizen Scientists' Help". NASA. Retrieved 17 May 2019.
  5. Anderson, P. C.; Heelis, R. A.; Hanson, W. B. (1991). "The ionospheric signatures of rapid subauroral ion drifts". Journal of Geophysical Research. 96 (A4): 5785. Bibcode:1991JGR....96.5785A. doi:10.1029/90JA02651.
  6. He, Fei; Zhang, Xiao-Xin; Chen, Bo (June 2014). "Solar cycle, seasonal, and diurnal variations of subauroral ion drifts: Statistical results". Journal of Geophysical Research: Space Physics. 119 (6): 5076–5086. Bibcode:2014JGRA..119.5076H. doi:10.1002/2014JA019807.
  7. ^ McRae, Mike. "Everyone, Meet 'Steve' – A Weird Type of Aurora We've Never Seen Before". ScienceAlert. Retrieved 17 May 2019.
  8. Skibba, Ramin (15 March 2018). "Meet 'Steve,' a Totally New Kind of Aurora". National Geographic. National Geographic. Retrieved 17 May 2019.
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