Analysis of the effects of zonal averaging on reaction rate calculations in two‐dimensional atmospheric models

The usual assumption by which chemical reaction rates are calculated in two‐dimensional atmospheric models is by using a product of zonal means of rate coefficients and constituent concentrations rather than the rigorous zonal mean of the corresponding products. This assumption has been tested for the reactions O + NO2 → NO+ O2 and NO + O3 → NO2 + O2 using mapped limb infrared monitor of the stratosphere data from the Nimbus 7 satellite and found to be quite satisfactory for winter 1979 at 60°N in the upper stratosphere. Relative differences between the two‐dimensional averaged rate and the more rigorous rate, calculated from the full, longitudinally varying temperatures and mixing ratios, were small (usually below 5%) and exceeded 15% only during times of strong dynamical activity. At those times or locations where stratospheric circulation is primarily zonal, the two averages agreed to within a few percent.