REGIONS: THE 12.09.1999 EVENT

I. M. Chertok, V. V. Grechnev, A. M. Uralov

Considering the 12.09.1999 event as an example, we analyze manifestations of large-scale disturbances associated with coronal mass ejections (CMEs) caused by filament eruptions outside of active regions. The analysis is based on H-alpha filtergrams, extreme ultraviolet and soft X-ray images as well as coronagraphic data. The filament eruption occurred in relatively weak magnetic fields, but it was accompanied by larger-scale phenomena than flare events do. The eruption was followed by the development in several hours of a large-scale arcade, whose bases were expanding flare-like ribbons. The volume of the event was bounded by an 'EIT wave', which was quasi-stationary at the solar surface, and expanded above the limb. The event was not impulsive; thus, the 'EIT wave' above the limb was a magnetic structure, which we identified as a frontal structure of a CME based on the coincidence of their shapes, structural details, and kinematics. Within the area of the event, three kinds of dimmings were observed, whose nature was (a) plasma evacuation, (b) plasma heating and its subsequent evacuation, and (c) absorption of emissions in a system of filaments activated by the eruption. The fact that a dimming appeared due to the plasma heating was revealed from soft X-ray data, whereas four EIT channels did not demonstrate this. Thus, a question arises about the correctness of some conclusions drawn previously from EIT data only. Transformations of magnetic fields due to the eruption occurred also inside a stationary coronal hole adjoining the area of the event. A CME expands self-similarly, with a rapidly decreasing acceleration, that is not taken into account by a polynomial fit, which is widely used.