Regensburg 2007 – scientific programme

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SYEE: Symposium Energy and Extraterrestrial Influences on the Climate

SYEE 1: Symposium: Energy an Extraterrestrial Influences on the Climate

SYEE 1.3: Invited Talk

Tuesday, March 27, 2007, 11:30–12:15, H46

Effects of the 11-Year Solar Cycle on the Atmosphere from the Surface to the Lower Thermosphere — •Marco A. Giorgetta, H. Schmidt, J. Kieser, and G.P. Brasseur — Max Planck Institute for Meteorology, Bundesstr.53, D-20146 Hamburg

The climate on Earth shows a broad spectrum of temporal and spatial variability resulting from internal dynamics or from external forcing. One such external factor is the variability of the solar irradiation at the top of the atmosphere induced by variations in the solar activity, as observed in the 11-year solar sunspot cycle, in the 27 day solar rotation signal or in particle events. The aim of this study is to quantify effects of the solar 11-year cycle on circulation, temperature and chemical composition of the atmosphere, and to put these signals into relation to other variations. For this purpose we employ the HAMMONIA whole atmosphere model, which is a global climate model that extends from the surface to the lower thermosphere, including physical and chemical processes. The high vertical extension of the HAMMONIA model allows the analysis of solar signals from the lower thermosphere, where for example temperature differences are very strong ( 500K), to smaller dynamical and chemical signals in the mesosphere and stratosphere, and weak signals in the troposphere. The HAMMONIA experiments can confirm the formation of primary ozone and temperature signals in the upper stratosphere and secondary signals in the lower tropical stratosphere, the latter mostly during boreal winter. This can be explained by the modification of the propagation conditions for planetary waves from the extratropical troposphere to the tropical upper stratosphere, resulting in a modified Brewer-Dobson circulation including a reduced upwelling in the tropical lower stratosphere for solar maximum conditions. Reduced upwelling results then in higher temperature and ozone mixing ratios, as similarly derived from observational analyses.