The Large-Scale Coronal Field Structure and Source Region Features for a Halo Coronal Mass Ejection

Details The Large-Scale Coronal Field Structure and Source Region Features for a Halo Coronal Mass Ejection The Large-Scale Coronal Field Structure and Source Region Features for a Halo Coronal Mass Ejection

Jun 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apj...572..580w&link_type=abstract

The Astrophysical Journal, Volume 572, Issue 1, pp. 580-597.

Astronomy and Astrophysics

Astronomy

57

Sun: Corona, Sun: Flares, Sun: Magnetic Fields, Sun: Particle Emission, Sun: Uv Radiation, Sun: X-Rays, Gamma Rays

Scientific paper

On 1998 May 2 a class X1/3B flare occurred at 13:42 UT in NOAA Active Region 8210 near disk center, which was followed by a halo coronal mass ejection (CME) at 15:03 UT observed by SOHO/LASCO. Using the boundary element method (BEM) on a global potential model, we reconstruct the large-scale coronal field structure from a composite boundary by SOHO/MDI and Kitt Peak magnetograms. The extrapolated large field lines well model a transequatorial interconnecting loop (TIL) seen in the soft X-ray (SXR) between AR 8210 and AR 8214, which disappeared after the CME. The EUV Imaging Telescope (EIT) observed the widely extending dimmings, which noticeably deviate from the SXR TIL in position. We find that the major dimmings are magnetically linked to the flaring active region but some dimmings are not. The spatial relationships of these features suggest that the CME may be led by a global restructuring of multipolar magnetic systems due to flare disturbances. Mass, magnetic energy, and flux of the ejected material estimated from the dimming regions are comparable to the output of large CMEs, derived from the limb events. At the CME source region, Huairou vector magnetograms show that a strong shear was rapidly developed in a newly emerging flux region (EFR) near the main spot before the flare. Magnetic field extrapolations reveal the presence of a ``bald patch'' (defined as the locations where the magnetic field is tangent to the photosphere) at the edge of the EFR. The preflare features such as EUV loop brightenings and SXR jets appearing at the bald patch suggest a slow reconnection between the TIL field system and a preexisting overlying field above the sheared EFR flux system. High-cadence Yohkoh/SXT images reveal a fast expanding motion of loops above a bright core just several minutes before the hard X-ray onset. This may be a precursor for the eruption of the sheared EFR flux to produce the flare. We propose a scenario, similar to the ``breakout'' model in principle, that can interpret many observed features.

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