Neutral atmospheric composition measurements were obtained by the Esro 4 gas analyzer during a series of geomagnetic storms in late February 1973. Complemented by ground-based ionosonde data, these measurements show a complex latitudinal and longitudinal structure of the storm-associated disturbances in the upper atmosphere. Specifically, a strong depression of the O/N2 ratio developed and persisted for several consecutive days above the Australian-African area. It was distinguished by a fairly sharp eastward boundary near 180¿E longitude. This mid-latitude disturbance zone was distinctly separated from strongly disturbed regions at higher latitudes. It is suggested that the energy causing this mid-latitude disturbance was deposited primarily at altitudes below 150 km. Because of the long diffusion time constants in the lower thermosphere this can account for the persistence of the phenomena observed at F2 layer heights.