COMPOSITION AND WINDS IN THE EARTH'S LOWER THERMOSPHERE

Under the Atmosphere Explorer project an Open Source Mass Spectrometer (OSS) from the University of Minnesota was placed into Earth orbit onboard each of the three satellites in the program. These spectrometers were designed to measure the neutral atmospheric composition in the lower thermosphere. Some of the results from analysis of the data provided by these spectrometers is presented here. Special effort was made to analyze measurements near and below 200 km altitude.;The last part of the analysis presented is a calculation of the global scale, horizontal neutral wind field at 200 km. Due to data limitations the wind calculations are restricted to only the horizontal components and the equatorial region. Composition measurements from the OSS spectrometers provide the total number density in a single fluid model of the pressure driving force. Similar wind calculations are repeated using total number densities and temperatures predicted by the MSIS and the Esro 4 thermospheric models. The major difference between these three wind calculations is the large enhancement of atomic oxygen in the winter hemisphere during early morning observed by the OSS spectrometers on Atmosphere Explorer. The calculations indicate that the normally expected summer to winter flow, reproduced by the MSIS and Esro 4 based models, may reverse during a significant portion of the day producing a net winter to summer flow at equatorial latitudes and 200 km altitude.;The second satellite in the series was placed into a polar orbit and provided measurements largely characterized by summer to winter differences during a time of low solar and geomagnetic activity. Neutral composition measurements determined from this satellite compare favorably to other reported measurements from satellite, rocket, and ground based instruments. Also shown is a detailed comparison at 150 and 200 km between these measurements and neutral composition as predicted by three current thermospheric models: CIRA 72, Esro 4, and MSIS. None of the models are based on the measured composition values from the OSS spectrometer on this satellite. The comparisons form an independent check on the predictive performance of these models for a limited range of the model parameters.