The simultaneous measurements of neutral composition both from Esro 4 and from Aeros-A have provided a complementary set of data for studying the temporal and spatial characteristics of the thermosphere during a major geomagnetic storm on April 1--2, 1973. From the correlative studies of Ar and N2 number densities, the magnetic index ap, and ground-based magnetograms, it is found that the index ap only reflects the gross features of the atmospheric disturbances. Superposed on the global component are localized regions of 'hot spots' which appear correlated with ground-based magnetograms. Because of these localized disturbances the interpretation of the atmospheric response to geomagnetic storms becomes ambiguous.