Overall magnetic field configuration before the August 31 eruption. Top left: Kanzelhöhe Hα image acquired on August 27 showing the relative position of the filament (surrounded by a red line) and the active region (white circle). Top right: SOHO/MDI photospheric magnetic field map on August 27 showing the position of the filament (red line) with respect to the different magnetic field polarities and to the magnetic neutral line (yellow line, from the Wilcox Solar Observatory). Bottom: potential field extrapolations as derived for August 24 (left) and August 28 (right) showing the position of closed fieldlines overlying the active region and the Hα filament (red line).