The sequence of ionograms during a solar flare occurred on May 13, 2013. The ionograms of Kokubunji and Okinawa are shown on the left and right of the pictures, respectively. The upper panels are the results before the flare began (1:45 UT), the middle panels are the results at the flare peak (2:15 UT), and the lower panels are the results at the end of the SWF (3:45 UT). The green curve and horizontal line represent the signal reflected in the ionosphere, and the vertical line is noise.