Vertical phase and group velocities of internal gravity waves derived fromionograms 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 t o a sequence of ionograms recorded by the digisonde portable sounder in Tai wan and find numerous waves occuring in the ionosphere during the solar ecl ipse 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 ledg e are about 100 mis in the downward and upward directions, respectively. Th e associated group velocities below and above the ledge are found to be abo ut 10 m/s in the downward and upward directions, respectively, which indica tes that during the solar eclipse the wave source is near the F1-ledge. (C) 1999 Elsevier Science Ltd. All rights reserved.