Emergence and Drastic Breakdown of a Twisted Flux Rope to Trigger Strong Solar Flares in NOAA Active Region 9026

Abstract

An emerging twisted flux rope model to explain the drastic evolution of a flare-productive NOAA Active Region 9026 is presented. The drastic changes in the-type sunspot configuration were found to start shortly before the big flares of 2000 June 6: (1) rapid proper motions of sunspots started at the both sides of the central sunspot about 7 hr prior to the strong flare activity, (2) the collapse of the central sunspot with its disintegration and partial disappearance started about 3 hr before the strong flare activity, (3) a switchback-shaped and strongly sheared magnetic neutral line was formed with intruding motions of sunspots into the opposite magnetic polarities, and (4) the direction of the neutral line rapidly rotated clockwise at the same time when the switchback neutral line was formed. To explain these outstanding features of the sunspot evolution , we constructed a schematic model of an emerging twisted flux rope in which the central writhe helicity of the flux rope could be formed by continuous transformation of the twist helicity by means of the kink instability in the course of its emergence through the convection zone.