Tracer simulation using a global general circulation model: Results from a midlatitude instantaneous source experiment

Abstract An 11-level general circulation model with seasonal variation is used to perform an experiment on the dispersion of passive tracers. Specially constructed time-dependent winds from this model are used as input to a separate tracer model. The methodologies employed to construct the tracer model are described. The experiment presented is the evolution of a hypothetical instantaneous source of tracer on 1 January with maximum initial concentration at 65 mb, 36°N, 180°E. The tracer is assumed to have no sources or sinks in the stratosphere, but is subject to removal processes in the lower troposphere. The experimental results reveal a number of similarities to observed tracer behavior, including the average poleward-downward slope of mixing ratio isopleths, strong tracer gradients across the tropopause, intrusion of tracer into the Southern Hemisphere lower stratosphere, and the long-term interhemispheric exchange rate. The model residence times show behavior intermediate to those exhibited for parti...