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We report the first statistical analysis of stable auroral red (SAR) arc detachments from the main auroral oval, using 630-nm all-sky cooled-Charge Coupled Device images obtained at Athabasca (magnetic latitude = 61.7 degrees N), Canada. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of ring current particle injection in the inner magnetosphere. We analyzed all-sky images obtained for 11 years from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur in the premidnight sector, indicating the ring current ion drift to the dusk sector. The SAR arc detachments also tend to occur at the beginning of the substorm recovery phase, suggesting that the SAR arcs detach from the main oval as the main auroral oval returns to higher latitudes. The equatorward velocities of detached SAR arcs are from -100 m/s (poleward) to +200 m/s (equatorward), corresponding to magnetospheric electric fields from -1 to +2 mV/m.

Plain Language, Summary Stable auroral red (SAR) arcs are the optical emissions caused by low-energy electron precipitation into the ionosphere from the inner magnetosphere close to the earth. In this paper, we report the first statistical analysis of SAR arc detachments from the main auroral oval, using all-sky cooled-Charge Coupled Device images measured at a wavelength of 630.0 nm obtained at Athabasca, Canada, which is located at latitudes just lower than the auroral zone latitudes. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of high-energy particle injection in the inner magnetosphere. We analyzed 11-year all-sky images from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur premidnight, indicating the high-energy ion drift to the dusk sector. We also found that the SAR arc detachments tend to occur at the beginning of the substorm recovery phase. This likely indicates that the SAR arcs detach from the high-latitude aurora as the main aurora returns to higher latitudes at the beginning of the recovery phase. The equatorward velocities of detached SAR arcs are also estimated from the analysis.