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 numerical model we use is the HAMMONIA general circulation and chemistry model developed at MPI-M. It is one of very few 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 in general increasing with altitude and which depend in particular on up- and downward coupling processes in the atmosphere. The simulations concern the influence of solar variability on different timescales and the coupling phenomena in the atmosphere related to these timescales. Within the first two phases of this project we have studied separately 1) the influence of the 11-year sun spot cycle and its interactions with the quasi-biennial oscillation in the stratosphere and mesosphere, 2) the influence of the 27-day solar rotational variation and 3) the influence of precipitating particle events and the role of ions in the response to solar variability. Main issues in the third phase of ARTOS will be a) the relative importance of precipitating particles and radiation variations in different atmospheric height regions during the last about 50 years, and b) the role of ocean-atmosphere interactions in solar-terrestrial coupling.