Middle atmosphere density data and comparison with models

Abstract Density data derived from measurements of the drag on twelve reentering Shuttle vehicles within the altitude range 40 to 97km have been compared with several models. There are no significant differences between the values of the several models, but the Shuttle data for a number of flights are significantly different from the models. Possible reasons for this are discussed. The variation of density with latitude is, in general, well represented by the models, but the seasonal dependence in the empirical models needs to be improved. Some flights show marked departures from the models at the higher altitudes (generally above 70km). Some possible causes of these departures, including convective activity and gravity waves, are discussed.