A procedure is developed to derive the vertical phase and group velocities of waves from measurements of ionograms. We apply the developed procedure to a sequence of ionograms recorded by the digisonde portable sounder in Taiwan and find numerous waves occuring in the ionosphere during the solar eclipse of 24 October 1995. A detailed analysis of an 87-min period wave shows that the vertical phase velocities of the wave below and above the F1 ledge are about 100 mis in the downward and upward directions, respectively. The associated group velocities below and above the ledge are found to be about 10 m/s in the downward and upward directions, respectively, which indicates that during the solar eclipse the wave source is near the F1-ledge. (C) 1999 Elsevier Science Ltd. All rights reserved.
JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS