Build-up of a CME and its Interaction with Large-Scale Magnetic Structures

VAN DRIEL-GESZTELYI, L.; GOFF, C.P.; DÉMOULIN, P.; CULHANE, J.L.; KLEIN, K.-L.; MANDRINI, C.H.; MATTHEWS, S.A.; HARRA, L.K.; KUROKAWA, H.

Praga

Congreso; 26th IAU General Assembly - Joint Discussion 3: Solar Active Regions and 3D Magnetic Structure; 2006

IAU

Introduction: A series of flares (GOES class M, M and C) and a CME were observed on 20-JAN-2004 occurring in close succession in NOAA 10540. Types II, III and a N radio bursts were associated. We investigate the link between the flares (two impulsive flares followed by an LDE) and the CME as well as the origin of the rare decametric N-burst. Methods: We use the combined observations from TRACE, SOHO/EIT, H-alpha images from Kwasan Observatory, SOHO/MDI magnetograms, GOES and radio observations from Culgoora and Wind/WAVES as well as magnetic modelling to understand the complex development of this event. Results: We link the first two impulsive flares to tether-cutting reconnections and the launch of the CME, while the last of the flares, an LDE, to the relaxation phase following forced reconnections between the erupting flux rope and neighbouring magnetic field lines. We show that reconnection with the magnetic structure of a previous CME, launched about 8 hours earlier, injects electrons into open field lines having a local dip and apex of about 6 solar radii height. The dipped shape of these field lines was due to large-scale magnetic reconnection between expanding magnetic loops and open field lines of a neighbouring streamer. This particular situation explains the observed decametric N burst. Discussion: This complex observation shows that impulsive quadrupolar flares can be eruptive, while an LDE may remain a confined event. We find that reconnection forced by the expanding CME structure is followed by a relaxation phase, when reconnection reverses and restores some of the pre-eruption magnetic connectivities. The observed decametric N-burst was caused by the interaction of two CMEs and reconnection of their expanding magnetic field with neighbouring streamer field lines - a very particular interplay, which explains why N-bursts are so rare.