Data from the Atmosphere Explorer-C satellite clearly exhibit wavelike variations in neutral composition, ion density, and electron temperature, variations which appear to be a general feature of the atmosphere. The neutral constituents do not exhibit uniform wave characteristics, since the density variations of argon are approximately twice those of molecular nitrogen, which range between 5 and 15%. Helium structure, on the other hand, has about one half the amplitude of the N2 variation and is 180° out of phase with the two heavy gases most of the time. The waves evident in the ion density are nearly in phase with the heavy neutrals, while the electron temperature variations are predominantly out of phase with those in the ion density. Scale sizes for the structure range from a few tens of kilometers to several hundred kilometers. A simple model is suggested to explain the neutral composition results, wherein the enhancements in the major gas densities are in phase with the vertical component of the perturbation velocity of the gas. The vertical velocity modifies the composition by transporting parcels of air to higher or lower regions where the composition is different. The phase relationship between the density and velocity implies phase velocities (assuming that these are gravity waves) of the order of 500 m s−1.