Overview of observations taken at 09:44:37 UT. Panel a: continuum at 400 nm; panel b: B_z as inferred from a Milne–Eddington inversion of the Fe I 603.1 nm and 630.2 nm lines, the colour scale ranges from −2.0 kG to 1.4 kG; panel c: horizontal magnetic field from the same inversion, the colour scale ranges from 0 kG to 1.3 kG; panel d: Ca II K image in the K_1v minimum of the average line profile; panel e: Ca II K at nominal line centre; panel f: Hα at nominal linecentre; panel g: blue wing of the Ca II 854.2 nm line; panel h: Ca II 854.2 nm at nominal line centre. The colour scales are clipped to exclude the 0.5% darkest and brightest pixels. The coloured plusses in panel d indicate the locations for which line profiles are shown in Figs. 2 and 3; the location of the xy subfield shown in Fig. 8 is indicated by a white box; the location of the timeslice shown in Fig. 9 with a blue line. An animated version of this figure showing the entire time sequence is available online.