Propagating disturbances. (a) HRI_EUV image of plume 2. Positions at different distances from the base region are marked with diamonds. The intensities along the slits perpendicular to the stream direction at these positions are fitted by a Gaussian function. (b) and (c) show the peak and FWHM of the fitted Gaussian functions, as a function of the distance along the PD, at three instances (each separated by 20 s; as identified with different colors). Same as Figure 6c and d, the error of intensity in (b) comes from the detector readout noise and dark current and the error of width is derived from the Gaussian fitting.