Recent improvements in our knowledge of neutral atmosphere structure from satellite drag measurements

Observational results on the density in the thermosphere and lower exosphere (i.e., within the altitude range from about 150 to about 1000 km) are discussed in this paper. Most observational results on total gas density were obtained from orbital drag and more recently also from in-situ drag analysis. The primary parameter measured is atmospheric density, with temperature as a secondary structural parameter deduced with the help of theory and/or atmospheric models. Both the merits and shortcomings of the drag analysis method are outlined in view of a comparison of temperature deduced from total density and kinetic gas temperature measured by incoherent scatter. Recent improvements of our knowledge of the known density variations are presented.