Evolution of Vector Magnetic Field and White-Light Flares in a Solar Active Region (NOAA 6659) in 1991 June

Abstract

view Abstract Citations (41) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolution of Vector Magnetic Field and White-Light Flares in a Solar Active Region (NOAA 6659) in 1991 June Zhang, Hongqi ; Ai, Guoxiang ; Yan, Xu ; Li, Wei ; Liu, Yang Abstract The active region of 1991 June, NOAA 6659, was the most prolific white-light flare-producing region in recent history. About five white-light flares were observed in the active region. We present here the observational results on photospheric vector magnetic and velocity fields of this region obtained at the Huairou Solar Observing Station of the Beijing Astronomical Observatory and discuss the evolution of the magnetic fields and its relation to the powerful (white-light) flares. The salient characteristic of this active region is that it was a great (5-group, dominated by spots of preceding (p) polarity. The structures of following (f) polarity were almost around them, forming some magnetic gulfs and islands. Sites of homologous white-light flares on June 4, 6, and 9 occurred at both sides of the magnetic neutral line and almost at the same place in the active region, where the gradient of the longitudinal field was about 0.3-0.5 G km-1 and the horizontal components of the field, relative to the solar surface, were almost parallel to the neutral line due to the shear of the magnetic field. After analysis of a series of monochromatic images of Stokes parameters Q, U, and V with high spatial resolution, the following newly observed phenomena were found: (1) In this δ-region, some of the magnetic flux showed inverted polarity, and the longitudinal components of the emerging flux were aligned in fibril-like features whose small angles were relative to the horizontal components of the field on the solar surface, where the lines of force were highly sheared. (2) Before and after powerful (white-light) flares, the obvious change of vector magnetic fields occurred at the magnetic neutral line near the sites of these flares. The white-light flares probably are caused by the violent motion of the photospheric lines of force. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173861 Bibcode: 1994ApJ...423..828Z Keywords: SUN: FLARES; SUN: MAGNETIC FIELDS full text sources ADS |