Variation in the intensity of the main component of the O iv 1401 Å line in the region that showed a supersonic downflow (first panel from the top), together with density inferred from the ratio of the O iv 1400 Å and 1401 Å lines (second panel). The variation of the intensity of the satellite line at 1401 Å (third panel) and the density from the ratio of the satellite lines at 1400 Å and 1401 Å are shown in the third and fourth panels, respectively. The horizontal lines mark the boundaries of the regions given in Fig. 1, where the dashed line indicates Point C.