Relative density variations at 120 km derived from tidal wind observations made by the UARS/WINDII instrument

The empirical modelling of the density and composition of the Earth's thermosphere ideally requires a data set having a homogeneous distribution as a function of latitude, altitude, time, solar and magnetic activity. This is far from being achieved. Algorithms describing the mean atmospheric properties are used in which coefficients are determined from available data. This procedure is efficient above 180 km, but may generate artefacts at a lower altitude. For the purpose of satellite aerobraking, densities are required as low as 120 km. Hence better boundary conditions are needed for empirical thermosphere models such as drag temperature model (DTM94) (Berger et al., 1998). The WINDII experiment placed on board the upper atmosphere research satellite has extensively observed the atmospheric tides in the lower thermosphere. These observations being consistent with the tidal theory allow the derivation of the relative density variations at 120 km which will be used as boundary conditions to improve DTM94. (C) 2002 Elsevier Science Ltd. All rights reserved.