Phase path variations of F2 region echoes on 5.6 MHz over Waltair (17¿ 43'N; 83¿ 18'E) are found to exhibit prominent short-period reversals on some occasions during summer evening hours. The observed waves have periods in the range of 0.5 to about 5 min. The spectral content of the ionospheric waves is found to vary from one event to another. These disturbances are apparently associated with severe local thunderstorms in the troposphere and are interpreted as ionospheric manifestations of acoustic waves generated in the storm sources. The mechanical oscillations excited during the pulsating growth of a thundercloud are the likely source of the observed ionospheric disturbances. A simple model for the generation of acoustic waves by the developing thunderstorms is suggested.