Astronomy:Subauroral ion drift
A subauroral ion drift (SAID), also known as a polarisation jet, is an atmospheric phenomenon driven by substorms in the Earth’s magnetosphere.[1] First discovered in 1971,[2] 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[3] suggested the first link between this optical emission’s occurrence and that of an extremely fast and hot SAID event.[4]
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.[1] 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.[5] The exact characteristics of SAID events appear to have solar cycle, seasonal, and diurnal dependences.[6]
Although studied for decades, prior to the formal discovery of STEVE, SAIDs had never been associated with an optical emission.[7] STEVE was associated with a particularly extreme SAID, with a velocity over twice the norm and 100 K hotter.[7] STEVE has presented a new way for scientists, including citizen scientists, to study SAIDs.[8]
References
- ↑ 1.0 1.1 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. doi:10.1029/GL006i008p00657. Bibcode: 1979GeoRL...6..657S.
- ↑ 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.
- ↑ MacDonald, Elizabeth A.; Donovan, Eric; Nishimura, Yukitoshi; Case, Nathan A.; Gillies, D. Megan; Gallardo-Lacourt, Bea; Archer, William E.; Spanswick, Emma L. et al. (14 March 2018). "New science in plain sight: Citizen scientists lead to the discovery of optical structure in the upper atmosphere". Science Advances 4 (3): eaaq0030. doi:10.1126/sciadv.aaq0030. PMID 29546244. Bibcode: 2018SciA....4...30M.
- ↑ Patel, Kasha (14 March 2018). "Mystery of Purple Lights in Sky Solved With Citizen Scientists' Help". https://www.nasa.gov/feature/goddard/2018/mystery-of-purple-lights-in-sky-solved-with-help-from-citizen-scientists. Retrieved 17 May 2019.
- ↑ 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. doi:10.1029/90JA02651. Bibcode: 1991JGR....96.5785A.
- ↑ 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. doi:10.1002/2014JA019807. Bibcode: 2014JGRA..119.5076H.
- ↑ 7.0 7.1 McRae, Mike. "Everyone, Meet 'Steve' – A Weird Type of Aurora We've Never Seen Before" (in en-gb). https://www.sciencealert.com/aurora-named-steve-explained-subauroral-ion-drift. Retrieved 17 May 2019.
- ↑ Skibba, Ramin (15 March 2018). "Meet 'Steve,' a Totally New Kind of Aurora" (in en-gb). National Geographic. https://www.nationalgeographic.co.uk/science-and-technology/2018/03/meet-steve-totally-new-kind-aurora. Retrieved 17 May 2019.
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