MHD simulation’s evolution of the MFLs of the sheared arcade (in yellow). The bottom boundary is the magnetogram plotted in Fig. 1. Important is the formation of the flux rope (panels d–f), which is evident from the appearance of a twist value that is greater than 1 (in blue). As described in the text, t has units of 1 minute, with t = 0 corresponding to 21:24 UT. An animation of this figure is available online.