Plasma lines enhanced by HF radio waves have been used as a tracer of electron density fluctuations in the ionosphere. Both the intensity and the altitude of these plasma lines have been measured with very short time and range resolution. The power spectrum of the range variations indicates a power law dependence with a spectral index of -2.0 over periods of a few minutes to about 8 s; corresponding amplitudes are greater than 500 m to ~70 m. Instability and turbulent mechanisms seem to be responsible for the dissipation of large-scale irregularities to form continuously smaller scale sizes. Furthermore, isolated peaks of about 2- to 6-s periods with amplitudes of about 15--90 m ahve been observed on several occasions. The possible source of these fluctuations could be sound waves ducted in the ionosphere.