Observation and modelling of the upper atmospheric density and winds and their dependence on the geomagnetic conditions

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The state of the thermosphere and its temperature distribution are influenced by many factors. This level of the atmosphere is nowadays of great importance since all satellites in low-Earth orbit and manned spacecraft are flying at these altitudes. A special characteristic of the upper atmosphere is the ionisation of part of its gaseous particles. While the ionised component has been studied intensively during the past decades, the investigation of the neutral atmosphere has suffered greatly due to the lack of good observations in the thermosphere. This has changed significantly after the launch of the CHAMP satellite. It is generally assumed in models that the thermospheric structure is mainly controlled by the EUV solar flux, and the magnetic activity should play a minor role. Our recent measurements, however, indicate that this is not the case. In this proposal we plan to investigate the importance of the ionosphere-thermosphere coupling for the dynamics of the upper atmosphere at high latitudes. The study will be based on observations from CHAMP and the EISCAT radar facilities. We are focusing on the auroral region, where most of the Joule heating occurs. Our final aim is it to characterize the ionospheric heating mechanism which causes thermospheric density enhancements and drives winds. The roles of solar wind input and EUV solar radiation shall also be identified.