Extended Data Fig. 2: Magnetic field, current density and decay index around the eruption onset.
a, Current density on the slice of x = 0 at the time when the MFR first forms during the eruption (that is, t = 221 min 33 s). The black curves are projection of magnetic field lines on the slice. The lower arrow denotes the axis of the MFR. The upper arrow denotes the critical height of torus instability (TI). b, From top to bottom are shown for current density, magnetic field component By, and decay index of By, respectively, along z axis (that is, the line with both x and y = 0). The black, magenta, and blue curves represent results for the initial potential field (t = 0), the field immediately prior to the eruption onset (t = 217 min), and the field at t = 221 min 33 s, respectively. In the middle panel, the thick vertical line colored in gray denotes the height at which the MFR is initially formed. In the bottom panel, the dashed horizontal line denotes the critical value (1.5) of decay index, and the dashed vertical lines denote the corresponding heights.
