On‐the‐Disk Development of the Halo Coronal Mass Ejection on 1998 May 2

Abstract

A halo coronal mass ejection (CME) was observed at 15:03 UT on 1998 May 2 by the Solar and Heliospheric Observatory Large-Angle Spectrometric Coronagraph. The observation of the CME was preceded by a major soft X-ray flare in NOAA Active Region 8210, characterized by a delta spot magnetic configuration and some activity in region 8214. A large transequatorial interconnecting loop (TIL) seen in the soft X-rays connected AR 8210 to a faint magnetic field region in the periphery of region 8214. Smaller loop systems were also connecting AR 8210 to other fainter bipolar magnetic structures, the interconnecting loop (IL) east of AR 8210 being one of the most visible. We present here a multiwavelength analysis of the large- and small-scale coronal structures associated with the development of the flare and of the CME, with emphasis placed on radio-imaging data. In the early phases of the flare, the radio emission sources traced the propagation paths of electrons along the TIL and the IL, which are accelerated in the vicinity of AR 8210. Furthermore, jetlike flows were observed in soft X-rays and in Hα in these directions. Significantly, the TIL and IL loop systems disappeared at least partially after the CME. An EUV Imaging Telescope (EIT) dimming region of similar size and shape to the soft X-ray TIL, but noticeably offset from it, was also observed. During the flash phase of the flare, new radio sources appeared, presenting signatures of destabilization and reconnection at discrete locations of the connecting loops. We interpret these as possible signatures of the CME liftoff on the disk. An Hα Moreton wave (blast wave) and an EIT wave were also observed, originating from the flaring AR 8210. The signatures in radio, after the wave propagated high into the corona, include type II-like emissions in the spectra. The radio images link these emissions to fast-moving sources, presumably formed at locations where the blast wave encounters magnetic structures. The opening of the CME magnetic field is revealed by the radio observations, which show large and expanding moving sources overlying the later-seen EIT dimming region.