Two Types of Confined Solar Flares

Abstract

With the aim of understanding the physical mechanisms of confined flares, we selected 18 confined flares during 2011–2017, and first classified them into two types based on their different dynamic properties and magnetic configurations. “Type I” confined flares are characterized by slipping reconnection, strong shear, and a stable filament. “Type II” flares have almost no slipping reconnection, and have a configuration in potential state after the flare. A filament erupts but is confined by a strong strapping field. “Type II” flares could be explained by 2D MHD models, while “type I” flares need 3D MHD models. Seven of 18 confined flares (∼39%) belong to “type I” and 11 (∼61%) are “type II.” The post-flare loops (PFLs) of “type I” flares have a stronger non-potentiality, but the PFLs in “type II” flares are weakly sheared. All the “type I” flares exhibit ribbon elongations parallel to the polarity inversion line (PIL) at speeds of several tens of km s −1 . Only a small proportion of “type II” flares show ribbon elongations along the PIL. We suggest that different magnetic topologies and reconnection scenarios dictate the distinct properties for the two types of flares. Slipping magnetic reconnections between multiple magnetic systems result in “type I” flares. For “type II” flares, magnetic reconnections occur in antiparallel magnetic fields underlying the erupting filament. Our study shows that “type I” flares account for more than one third of all the large confined flares, and should not be neglected in further studies.