Horizontal velocities of intensity and Doppler structures, integrated over a time interval of 52 min. From left to right: a) broad-band (WL) around 621 nm, b) Ca II 854.2 nm blue (−60 pm) wing, c) Ca II line centre, and d) Doppler structures. The black dashed line outlines the border of the chromospheric filamentary structure. The black bars at the beginning of the x-axis correspond to 1 km s^-1 (note that their length is three times longer for (a),b) than for (c),d)).