Temporal evolution of the X2.2 flare in active region NOAA 12673 on 6 September 2017. (a) The early stage of the flare in the total unsigned circular polarization (Stokes-V) of the Ca II 8542 Åline, showing the chromospheric imprint of the parasitic negative-polarity patch (black) impinging onto the positive patch (white) at heliocentric coordinates (510″,   − 240″). (b) The ribbons at the same time in a logarithmic Hα COCOPLOT. (c) The expanding flare ribbons and rotation of the parasitic polarity umbra. (d) The white light response in the Ca II K continuum is indicated by a red arrow. (e) A logarithmic Hα COCOPLOT near the peak of the flare, showing the expanded flare ribbons (red arrows), the formation of a small arcade to the left of the rotating umbra (blue arrow), and a filament (magenta) that runs from north to south between the flare ribbons (green arrow) and (f) the corresponding Ca II K COCOPLOT.