Oscillations of F2 layer at dawntime

Introduces an index derived from a rapid run ionograms that can be used to study the local effect of travelling ionospheric disturbances (TIDs). This index describes the occurrence of ionospheric oscillation better than any other traditional parameters deduced from ionograms. Following the passage of the solar terminator, the authors detected oscillations in the gravity waves range. These oscillations were superimposed on high frequency oscillations in the acoustic wave range that also exist during the night. This confirms that the solar terminator is able to generate AGWs observable as medium scale TIDs