Steve is a nighttime optical phenomenon shown to be associated with intense subauroral ion drifts (SAID). The phenomenon is described as a purple band of light equatorward of aurora and it is sometimes accompanied by periodic green emissions termed “picket fence”. There are several hypotheses on the physical mechanisms that could be causing Steve and the picket fence, but so far none has been fully established and It is not known whether the two phenomena are causally linked.
(B) Photograph of Steve taken around 05:53 UT on 16 September 2017 by Janis Smith (O2). The southward and zenith directions are labeled with S and Z respectively. Stars angularly co-located with the southern and northern edge Steve are marked with empty squares and triangles, respectively. Stars angularly co-located with the southern and northern edge of the picket fences are marked with lled squares and triangles, respectively. In both (A) and (B) the picket fence structures are enumerated for reference.
(C) The position of O1, O2, and Dale Eurich (O3) are shown along with a rough estimate of the location of a portion Steve.
New research is trying to advance the understanding of these mechanisms underlying Steve and the picket fence by narrowing down the altitude and latitude ranges in which they occurs. The study, supported by ESA Living Planet Fellowship project “The ionospheric signature of auroral and subauroral fast flows” was conducted by fellow William Archer together with scientists from University of Saskatchewan, University of Western Ontario, NASA/GSFC, The New Jersey Institute of Technology, University of Calgary and Alberta Aurora Chasers. The scientists interpreted simultaneous photographic observations of Steve taken hundreds of kilometers apart and concluded that Steve and the picket fence extend vertically along similar magnetic field lines, with Steve’s optical emissions ranging from 130 to 270 km in altitude and the picket fence’s emissions ranging from 95 to 150 km altitude.
The full report, titled “The Vertical Distribution of the Optical Emissions of a Steve and Picket Fence Event” has been accepted for publication in Geophysical Research Letters and is available at
DOI: 10.1029/2019GL084473
Featured image : Altitude profile estimated for Steve and picket fence based on triangulation under the assumption that both phenomena extend along the Earth’s magnetic field. This photograph was taken by Robert Downie from Berg Lake Campground, British Columbia, Canada around 5:53 UT on 16 September 2017