Characteristic behavior of SAR arc, STEVE and Red-Green arc during HILDCAA events

Abstract

Using 630.0 nm all-sky airglow imagers at Athabasca (Canada), Kapuskasing (Canada) and Nyr(Formula presented) l(Formula presented) (Finland), we present the first statistical analysis of the Stable Auroral Red (SAR) arcs, STEVE, and Red-Green (RG) arcs during High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events from 2011 to 2019. These optical phenomena are unique and relatively faint subauroral optical phenomena observed in the Earth’s upper atmosphere at subauroral latitudes. We discovered 25 subauroral optical phenomena (SAR arc, STEVE, and Red-Green arc) after analyzing all-sky images taken over the 9-years period. The arc detachments from the auroral oval typically occur in the premidnight sector, indicating ring current ion drift to the dusk sector. Out of total 12 HILDCAA events, from 2011 to 2019, more than 90 % were accompanied by at least one of these auroras. We also found that the auroras occurring during these HILDCAA events tends to happen predominantly during midnight hours. The occurrence rate of these auroras found to be much higher during HILDCAA events reaching to approximately 45 %, compared to previous statistical studies, including non–HILDCAA times. © 2026 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.