The ionospheric electron density at discrete heights is obtained with a 1-min sampling interval using the Arecibo radar for several runs in May 1974. These values are treated as time series in a spectral analysis. Assuming the ionization fluctuations are random traveling ionospheric disturbances, hence are excited by random gravity waves in the neutral atmosphere, the observed spectra are used (1) to compare with the theoretically computed transmittivity functions, where satisfactory agreement has been obtained, and (2) to make inference about the nature of the gravity wave velocity spectrum at the source, which suggests broad bandedness. At least in one case the data suggest the continuous cascading of energy into higher frequency components through a nonlinear process as the spectrum of waves propagates upward into the thermosphere.