A diabatic circulation experiment in a two‐dimensional photochemical model

A two‐dimensional photochemical model based on diabatic circulation has been used to simulate the behavior of N 2 O, CFCl 3 (F‐11), and CF 2 Cl 2 (F‐12). The circulation is based on estimates of net heating from the ground to 60 km. Eddy diffusion has been reduced with respect to other model studies with K zz = 2 × 10 3 cm 2 s −1 everywhere above 100 mbar. Resulting tracer profiles show reasonable agreement with measured profiles in the tropics and fall off much more sharply with altitude than those produced by models using larger values of K zz . The agreement obtained is at least as good as that obtained with adjustable, eddy diffusion parameters. The diabatic circulation treatment is more closely related to real physical processes and thus more easily interpreted. Diffusive mixing appears to be more important in determining the details of the tracer distributions than the basic morphology.