Cosmogenic 14 CO as tracer for atmospheric chemistry and transport
Advances in atmospheric chemistry research depend increasingly on the use of threedimensional (3-D) atmospheric transport and chemistry models. In this thesis the application of atmospheric 14CO measurements for evaluation of such models is systematically developed. Emphasis is on the simulated global distribution and seasonality of the hydroxyl radical (OH) and the stratosphere - troposphere exchange (STE). Modeling studies with two different 3-D models in various configurations are presented. One model is evaluated with standard methods, i.e., with simulations of SF6, CH3CCl3 and CFCl3. Next, uncertainties in the cosmogenic 14C source distribution and their implications for the 14CO application are studied. The influence of the variable solar activity on cosmogenic 14C production and atmospheric 14CO is investigated, as is the effect of solar proton event induced 14C production on atmospheric 14CO. Indications for this geophysical effect are derived from observations. Furthermore, a climatological zonally averaged seasonal cycle of 14CO at surface level is constructed from observations. Quantitative comparison with model simulations reveals important implications for the simulated STE and OH. This provides a possible explanation for the observed interhemispheric asymmetry of 14CO.
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