Steve (atmospheric phenomenon)

STEVE (Strong Thermal Emission Velocity Enhancement) is an atmospheric optical phenomenon that appears as a purple and green light ribbon in the sky, named in late 2016 by aurora watchers from Alberta, Canada. According to analysis of satellite data from the European Space Agency's Swarm mission, STEVE is caused by a 25 km (16 mi) wide ribbon of hot plasma at an altitude of 450 km (280 mi), with a temperature of 3,000 °C (3,270 K; 5,430 °F) and flowing at a speed of 6 km/s (3.7 mi/s) (compared to 10 m/s (33 ft/s) outside the ribbon). The phenomenon is not rare, but had not previously been investigated.[1][2][3] In August 2018, researchers determined that the phenomenon's skyglow was not associated with particle precipitation (electrons or ions) and, as a result, could be generated in the ionosphere.[4]

"STEVE" redirects here. For other uses, see steve (disambiguation).
'STEVE' on 17 August 2015 at Little Bow Resort, AB, Canada.

Discovery and naming

STEVE has been observed by auroral photographers for decades,[3] with some evidence to suggest that observations may have been recorded as early as 1705.[5] However, the first accurate determination of what STEVE is was not made until after members of a Facebook group called Alberta Aurora Chasers named it, attributed it to a proton aurora, and called it a "proton arc".[6] When physics professor Eric Donovan from the University of Calgary saw their photographs, he suspected that was not the case because proton auroras are not visible.[7] He correlated the time and location of the phenomenon with Swarm satellite data and one of the Alberta Aurora Chasers' photographers, Song Despins, whose photos are not shown on this page. She also included GPS coordinates from Vimy, Alberta, that helped Donovan link the data to identify the phenomenon.[1]

One of the aurora watchers, photographer Chris Ratzlaff,[8][9] suggested the name "STEVE" from Over the Hedge, an animated comedy movie from 2006, in which its characters chose that as a benign name for something unknown.[10] Reportage of the heretofore undescribed unusual "aurora" went viral as an example of citizen science on Aurorasaurus.[11][12]

Robert Lysak, during the fall meeting of the American Geophysical Union in December 2016, suggested "Strong Thermal Emission Velocity Enhancement" as a backronym of STEVE,[13] one that has since been adopted by the team at NASA Goddard Space Flight Center studying the phenomenon.[14]

Occurrence and cause

STEVE may be spotted closer to the equator than the aurora,[15] and as of March 2018 has been observed in the United Kingdom, Canada, Alaska, northern U.S. states, and New Zealand.[16] STEVE appears as a very narrow arc extending for hundreds or thousands of miles, aligned east–west. STEVE generally lasts for 20 minutes to an hour. As of March 2018, STEVE has only been spotted in the presence of an aurora. STEVE was not observed from October 2016 to February 2017, or from October 2017 to February 2018, leading NASA to believe that STEVE may only appear in certain seasons.[17]

A study published in March 2018 by Elizabeth A MacDonald and other co-authors in the peer-reviewed journal Science Advances suggested that STEVE accompanies a subauroral ion drift (SAID),[18] a fast-moving stream of extremely hot particles. STEVE marks the first observed visual effect accompanying a SAID.[17] In August 2018, researchers determined that the phenomenon's skyglow was not associated with particle precipitation (electrons or ions) and, as a result, could be generated in the ionosphere.[4]

Association with picket-fence aurora

STEVE often, although not always, is observed above a green, "picket-fence" aurora.[19][20] Although the picket-fence aurora is created through precipitation of electrons, they appear outside the auroral oval and so their formation is different from traditional aurora.[21] The study also showed these phenomena appear in both hemispheres simultaneously. Sightings of picket-fence aurora have been made without observations of STEVE.[22]

The green emissions seem to be related to eddies in the supersonic flow of charged particles, similar to the eddies seen in a river, which move more slowly than the other water around them. The green bars in the picket fence are moving more slowly than the structures in the purple emissions, and some scientists have speculated they could be caused by turbulence in the charged particles from space.[23]

See also

References
  1. McRae, Mike (24 April 2017). "Introducing Steve - a Newly Discovered Astronomical Phenomenon". ScienceAlert.
  2. "When Swarm Met Steve". ESA. 21 April 2017.
  3. American Geophysical Union (20 August 2018). "New kind of aurora is not an aurora at all". Physorg.com. Retrieved 2018-08-21.
  4. Gallardo-Lacourt, B.; Liang, J.; Nishimura, Y.; Donovan, E. (20 August 2018). "On the Origin of STEVE: Particle Precipitation or Ionospheric Skyglow?". Geophysical Research Letters. 45 (16): 7968. Bibcode:2018GeoRL..45.7968G. doi:10.1029/2018GL078509.
  5. Finnegan, James; Asher, David; Nezic, Rok; Byrne, Conor; Bailey, Mark (23 July 2018). "Historical observations of STEVE". The Observatory. 138: 227–245. arXiv:1808.01872. Bibcode:2018Obs...138..227B.
  6. "Meet Steve". European Space Agency. Retrieved 2017-04-24.
  7. "Aurora photographers find new night sky lights and call them Steve". BBC News. 23 April 2017.
  8. ""I propose we call it Steve until then" - Alberta Aurora Chasers". February 10, 2016.
  9. "Amateur Sky-Watchers Discover Celestial Phenomenon, Name It 'Steve'". 24 April 2017.
  10. "New atmospheric phenomenon named STEVE discovered by aurora watchers". ABC News. 24 April 2017.
  11. Rozell, Ned (2015-04-02). "Citizen science meets the aurora". University of Alaska Fairbanks Geophysical Institute.
  12. "7 Things to Know About "STEVE"". Aurorasaurus. 2017-03-14.
  13. Moravec, Jeff. "Meet Steve, a sky phenomenon coming into its own". StarTribune. MediaCompany. Retrieved 9 May 2019.
  14. "Meet 'Steve,' a Totally New Kind of Aurora". 2018-03-14. Retrieved 2018-03-22.
  15. Saner, Emine (2018-03-19). "'Steve': the mystery purple aurora that rivals the northern lights". the Guardian. Retrieved 2018-03-22.
  16. Skywatching, Samantha Mathewson 2018-03-15T22:47:11Z. "Help NASA Study 'Steve,' a Newfound Aurora Type". Space.com. Retrieved 2019-05-13.
  17. Garner, Rob (2018-03-14). "NASA Needs Your Help to Find Steve and Here's How". NASA. Retrieved 2018-03-22.
  18. MacDonald, Elizabeth A.; Donovan, Eric; Nishimura, Yukitoshi; Case, Nathan A.; Gillies, D. Megan; Gallardo-Lacourt, Bea; Archer, William E.; Spanswick, Emma L.; Bourassa, Notanee (2018-03-01). "New science in plain sight: Citizen scientists lead to the discovery of optical structure in the upper atmosphere". Science Advances. 4 (3): eaaq0030. Bibcode:2018SciA....4...30M. doi:10.1126/sciadv.aaq0030. ISSN 2375-2548. PMC 5851661. PMID 29546244.
  19. Andrews, Robin George (3 May 2019). "Steve the odd 'aurora' revealed to be two sky shows in one". National Geographic. National Geographic. Retrieved 4 May 2019.
  20. Nishimura, Y.; Gallardo‐Lacourt, B.; Zou, Y.; Mishin, E.; Knudsen, D.J.; Donovan, E.F.; Angelopoulos, V.; Raybell, R. (16 April 2019). "Magnetospheric signatures of STEVE: Implication for the magnetospheric energy source and inter‐hemispheric conjugacy". Geophysical Research Letters. 46 (11): 5637–5644. Bibcode:2019GeoRL..46.5637N. doi:10.1029/2019GL082460.
  21. Lipuma, Lauren. "Scientists discover what powers celestial phenomenon STEVE". AGU News. American Geophysical Union. Retrieved 4 May 2019.
  22. Dunlevie, James (2018-11-06). "Aurora Australis with bonus 'picket fence' wows southern lights chasers in Tasmania". ABC News. Australian Broadcasting Corporation. Retrieved 4 May 2019.
  23. "Aurora-chasing citizen scientists help discover a new feature of STEVE". phys.org. Retrieved 2020-11-14.
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