Atmospheric response time of cosmogenic 14CO to changes in solar activity


  • Patrick Jöckel,

  • Carl A. M. Brenninkmeijer,

  • Mark G. Lawrence


Carbon-14 monoxide is an unique tracer for certain important aspects of atmospheric chemistry and transport. Particularly, it may provide an independent means of testing model-based OH distributions and seasonality. The cosmogenic source strength of 14CO is inversely correlated with the solar activity. This time dependence demands a rescaling of 14CO measurements or model results to comparable conditions regarding the solar cycle, in order to achieve information on global distributions and trends of OH. For this rescaling, a two-parameter filter is derived using the three-dimensional global Model of Atmospheric Transport and Chemistry (MATCH). The filter function defines the atmospheric response time of the 14CO concentration to changes in the total cosmogenic 14CO source strength. The latitude dependence of the response time in addition to the atmospheric lifetime of the tracer provides useful information about the model's transport properties, especially about the role of stratosphere-troposphere exchange. It may serve as a direct indicator for possible solutions of the unresolved hemispheric asymmetry of the atmospheric 14CO concentration. The general concept can be applied as a diagnostic test for coupled changes in atmospheric transport and chemistry in models. Time series of 14CO measurements can provide this information about the real atmosphere.