Evolution of the eruptive event in different observables, viewed in the (x, z) plane at y = 0. The temporal evolution of the magnitude of the current density (a)–(c) is presented by the color scale. Contours (white: a–c, j–l; black: d–i) are at thresholds ﹩| {\boldsymbol{j}}| =1.1﹩, 3.0, and 6.0 and identify the inverted Y-shape. Arrows mark the B_x and B_z components of the magnetic field (a)–(f). The temporal evolution of B_y (d)–(f), defined by the blue-to-white color scale, is almost unipolar. The velocity derivative ﹩\partial {u}_{z}/\partial z﹩ (g)–(i) shows a clear change of sign in the inverted Y-shaped structure. The velocity components u_x, u_z are indicated by arrows (g)–(i). The temporal evolution of the magnetic field energy density (j)–(l) is presented by the color scale. Contours (black: (j)–(l)) are at thresholds B² = 3.0, 4.0, and 6.5. The dashed line box (j)–(l) marks the region of the increased magnetic energy density within the volume of the cusp that contains the flare loops (compare k and l). The animation begins at ﹩t=164{t}_{A}﹩ and ends at ﹩t=244{t}_{A}﹩.

(An animation of this figure is available.)

The video/animation of this figure is available in the online journal.