Multi‐Wavelength Imaging Observations of STEVE at Athabasca, Canada

Abstract

AbstractWe present the first multi‐wavelength imaging observations of strong thermal emission velocity enhancement (STEVE) using an all‐sky imager at Athabasca (magnetic latitude = 61.5°N), Canada. This study is based on three STEVE events which were accompanied by picket fence structures in the green‐line. Although the STEVE arc was dominant in 630 and 557.7‐nm, weak emissions were also found in other wavelengths including OI at 844.6, Hβ, Na, and the nominal background filter at 572.5‐nm. As observed at 630 and 557.7‐nm, the STEVE arc started as a faint arc close to the auroral oval and moved equatorward. The 557.7‐nm arc exhibited picket fence structure at later times after it moved equatorward. The picket fence was sometimes found to persist even after the 630‐nm arc had disappeared. During a particular event, the STEVE arcs in both the 630 and 557.7‐nm were found to carry a ribbon‐like motion moving along the arc. We have found that STEVE arcs are embedded in a region of weak diffuse auroral emissions. The STEVE arcs have sharp boundaries and these boundaries are different in red‐ and green‐line. The sharp decrease in the intensity at the immediate poleward edge of the STEVE arc appears as a “dark‐band” in the green‐line images. Based on the horizontal component of the geomagnetic field at Fort Smith (magnetic latitude 67.28°N), we find that the STEVE arc detachment, its equatorward motion, and its brightness coincided with changes in the magnetic activity during the recovery phase of a substorm.