When wave-induced diffusion is included in the equations governing acoustic-cravity wave propagation in an atmosphere in diffusive equilibrium, it is found that phase and amplitude relationships between the density fluctuations of individual atmospheric constituents agree with AE-C satellite observations of wavelike structure only over a narrow range of wave periods. For a 400 km horizontal wavelength, the observations are consistent with internal gravity waves of period 11.5-22 minute propagating at phase speeds 300-600 m/sec.