Fig. 8

Time variations in a solar X-ray flux, b fmin, c dfmin, and d maximum ionosonde signal at each frequency observed by VIPIR2 on July 23, 2016, e VIPIR2 ionograms at LT(= UT + 9 h) 10:45 (left) and 11:15 (right), f VIPIR2 signal intensities before SWF at LT 10:45 (black) and during SWF at 11:15 (red), and g their difference representing SWF absorption (blue), as a function of frequency. Absorption intensities estimated using Eq. (10) from Maeda and Inuki (1972) and twice Eq. (2) from Sato (1975) are shown by the green dashed and red lines, respectively, in Fig. 8g