Multi-Wavelength Imaging Observations of STEVE at Athabasca, Canada

We 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.