Coronal Loop Oscillations and Flare Shock Waves

Abstract

A statistical analysis of coronal loop oscillations observed by the Transition Region and Coronal Explorer (TRACE) shows that 12 of 28 cases were associated with metric type II bursts. The timing is consistent with the idea that in many cases the loop oscillations result from the passage of a large-scale wave disturbance originating in a flare in the nearby active region. The GOES classifications for these flares range from C4.2 to X20. Typically, the oscillating structures are not disrupted, implying that the disturbance has passed through the medium, which has returned to an equilibrium near that seen prior to the event. This is consistent with the Uchida interpretation of the disturbance as a weak fast-mode blast wave (i.e., a simple wave at a low Alfvénic Mach number) propagating in the ambient corona. We note that all 12 of the associated events were also associated with coronal mass ejections (CMEs) and conclude that the CME eruptions in these cases corresponded to only partial openings of the active-region magnetic fields.