A Survey and Statistical Study of Off-Limb Events Observed in SDO/HMI Continuum Intensity

Abstract

Several strong eruptive events that occurred near the solar limb were reported generating off-limb features detectable in the SDO/HMI’s continuum intensity. These observations offer new insights into the emission mechanisms of off-limb flaring loops, magnetic strength in the loops, and electron density distributions, among others. However, only a limited number of such events were reported, and it is unclear whether off-limb white-light features are popular or only associated with specific eruptions. In this study, we surveyed all the flaring events that occurred between May 2010 and August 2023 with a magnitude stronger than M2.0 and a heliographic longitude larger than \(65^{\circ }\). We found that among the 189 flares that met our selection criteria, 78 (41.3%) had off-limb features associated with them. Further statistical analysis showed, unsurprisingly, that the stronger the flare, the more likely it has an off-limb white-light feature, and the closer the flare is to the limb, the more likely an off-limb feature is detectable. We then categorized these off-limb white-light events into four types, closed-loop eruptions, open-loop eruptions, fast ejection, and flare arcades, and identified the events with visible flare ribbons. Coupling two examples of the white-light observations with simultaneous UV/EUV observations, we demonstrate the usefulness of the former in studying the flare dynamics and emission mechanisms. Our catalogue provides a rather complete list of the off-limb white-light events, which will benefit the community interested in studying such events.