Simulations of cosmogenic 14CO using the three-dimensional atmospheric model MATCH:: Effects of 14C production distribution and the solar cycle

Most atmospheric (CO)-C-14 is produced by cosmic rays in the lowermost stratosphere and upper troposphere. The main removal process for (CO)-C-14 is oxidation by OH radicals. Assuming that the spatial distribution of OH: is well known, (CO)-C-14 can be useful as a test-tracer for the transport properties of a three-dimensional chemical model. Conversely, if the transport schemes of the model are sufficiently realistic, in particular with respect to stratosphere-troposphere exchange, the OH distribution can be evaluated. In either case, it has to be assumed that the source of (CO)-C-14 is known in sufficient detail. Two presently available distributions of cosmogenic C-14 production are implemented into the Model of Atmospheric Transport and Chemistry (MATCH). The tropospheric (CO)-C-14 concentrations that are obtained are relatively insensitive to the source differences. The calculations for one source distribution are performed for solar minimum and solar maximum conditions. The spatial distribution of (CO)-C-14 is almost unaffected by the solar activity, and the absolute concentration levels can be scaled to the actual solar cycle conditions.