Atmospheric Dynamics and Magnetic Activity Associated With A Coronal Mass Ejection

Abstract

By using multi-wavelength observations, we explored the atmospheric dynamics and the surface magnetic activity in NOAA 9026, which were associated with the initiation of a halo coronal mass ejection (CME) on 6 June, 2000. In an interval of less than two hours, two X-class X-ray flares took place successively, each along with one eruption of a filament. However, only the second X-class flare which is characterized by a rather large-scale (larger than a general active region in area) EUV dimming was associated with the CME initiation. It seems that a flare with an extensive dimming is more likely to be CME-associated. We focused our study on the daily evolution of the vector magnetic field in this region from 4 to 9 June and have found the following results. (1) The gradual squeeze and cancellation of the opposite polarity magnetic fields are the main patterns of magnetic evolution. Moreover, there is a spatial coincidence between the sites of magnetic flux cancellation and the locations of the early filament activation and the flare brightenings. (2) The current system increased in the first two days and began to decrease at least ten hours before the CME initiation. It underwent dramatic disruption from 6 to 7 June. (3) The transverse component of the the vector magnetic field appeared helical in configuration. It changed from compact to loose and dissipated from a small to a large area. Here we suggest that although the first filament eruption and first flare were not in step with the CME initiation, they seem to be a part of the entire process. The observed evolution of the magnetic field implies a continuous transport of magnetic energy and complexity from the lower atmosphere to the corona. Moreover, the slow magnetic reconnection in the lower atmosphere, manifested as magnetic flux cancellation, and the helicity re-distribution, appear to play a key role in the energy build-up process of the flares and the initiation of the halo CME.