STEVE Events With FUV Emissions

Abstract

AbstractSTEVE, Strong Thermal Emission Velocity Enhancement, was often observed by ground‐based imagers in visible wavelengths and rarely detected by global FUV imagers. We present a new event, and revisit two reported STEVE events, that were observed by the DMSP/SSUSI FUV imager at O 135.6 nm, N2 LBHS, and LBHL emissions. Coincident particle and plasma drift observations showed that the events were associated with high ion drift speed, low ion density and no energetic particle precipitation. This is consistent with earlier findings (e.g., MacDonald et al., 2018, https://doi.org/10.1126/sciadv.aaq0030; Gallardo‐Lacourt et al., 2018a, https://doi.org/10.1029/2018ja025368, 2018b, https://doi.org/10.1029/2018gl078509; Archer et al., 2019). In this paper, several new features are identified: (a) Detection rates of FUV STEVE are much lower than that of visible STEVE; (b) The STEVE on 27 March 2008 covers 3‐hr local time with a length up to 2,700 km around 60° magnetic latitudes; (c) Different widths of STEVE observed in O 135.6 nm and N2 LBH images indicate a large altitude range in the STEVE FUV emissions; (d) The true ion (assuming O+) drift speeds during the 27 March 2008 STEVE event could be up to 20 km/s, well above the DMSP SSIES sensor limit. The kinetic energy of the high speed ions is larger than the excitation potential of the observed FUV emissions; (e) The requirement of such extreme high ion drift speed explains why FUV STEVE have been rarely observed, compared to the visible STEVE; (f) The three FUV STEVE events occurred during moderate geomagnetic activity; (g) Theses events were conjugate in both hemispheres.