Ground-based ionospheric sounding array observed gravity waves with wave periods of 13 to 28 minutes (mostly around 】3 minutes) and with horizontal phase velocities of 90 to 220 m/sec during tornadic storms, and gravity waves with wave periods of 2】to 25 minutes, and with horizontal phase velocities of 110 to 210 m/sec during hurricanes at the F-region ionospheric height. By using data on the neutral atmosphere and neutral wind profiles, a group ray .tracing computa* tion has been carried out in an attempt to locate the sources of these waves.