Use of on‐line tracers as a diagnostic tool in general circulation model development: 1. Horizontal and vertical transport in the troposphere

The use of passive on‐line tracers in a general circulation model (GCM) developmental process is discussed. CFC‐11 and 85 Kr are used to evaluate interhemispheric transport. It is shown that new boundary layer and convective parameterizations lead to reductions in the interhemispheric exchange times to values in close agreement with observations of little more than one year. Radon 222 is used to evaluate vertical mixing away from the surface. The new convection scheme produces smaller convective fluxes, which substantially reduce the high‐altitude concentrations of 222 Rn equatorward of 30° latitude. While this result is in better agreement with other models, scarcity of observations prevent any conclusion as to which formulation is more accurate. The effect of altered numerical schemes for solution of the momentum and energy equations in the GCM is shown to have little influence on the model's interhemispheric transport or vertical mixing. Finer vertical resolution increases convective mixing of 222 Rn somewhat and allows for larger pollution concentrations of CFC‐11 in the boundary layer. Employing on‐line passive tracers in the course of model development should allow for improvements in a GCM's horizontal and vertical fluxes and optimization of the model for atmospheric chemistry purposes.