Vertical phase and group velocities of internal gravity waves derived from ionograms during the solar eclipse of 24 October 1995

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 m/s 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.