The Atmospheric Response to Solar Variability: Simulations with a General Circulation and Chemistry Model for the Entire Atmosphere

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The goal of this project is to improve our knowledge on the response of the Earth¿s atmosphere to the variable input of the sun from the thermosphere to the surface by using a general circulation and chemistry model for the entire atmosphere. This will help to better constrain natural and anthropogenic causes of the observed climate trends. The simulations will concern the influence of solar variability on different timescales and the coupling phenomena in the atmosphere related to these timescales. Within the first two years of this project it is planned to study in more detail 1) the influence of the 11-year sun spot cycle and its interactions with the quasi-biennial and semi-annual oscillations in the stratosphere and mesosphere, 2) the influence of the 27-day solar rotational variation and its interactions with atmospheric waves, and 3) the influence of precipitating particle events and the role of ions in the response to solar variability. These issues are strongly linked. However, to understand the individual processes, they will be studied separately in the first phase of the project. Simulations will be performed with the HAMMONIA general circulation and chemistry model of the MPI for Meteorology. HAMMONIA is one of three models worldwide that treat dynamics, radiation and chemistry comprehensively for the entire atmosphere (up to 250 km). Therefore, it is a well suited tool for studying effects of solar variability which are expected to be strongest above the stratopause (50 km) and where the open questions concern in particular up- and downward coupling processes in the atmosphere.