Effect of computed horizontal diffusion coefficients on two-dimensional N20 model distributions

The sensitivity of the N20 distribution in our two-dimensional photochemical model to horizontal diffusion coefficients (both Kyy and Ky z values) has been explored. The residual circulation was computed using temperature data from the National Meteorological Center (NMC) and heating rates from Ro-senfield et al. (1987). The Kyy and Ky z values were computed from these same data using quasi-geostrophic potential vorticity. For comparison we also computed self-consistent Kyy values from our residual circulation. The use of either set of these diffusion coefficients produced substantial changes in the N20 distribution, especially in the middle to upper stratosphere and at high latitudes in the winter. In general, the changes lead to an enhanced transport of N20 to higher latitudes with the set of self-consistent Kyy values transporting the greatest amount of N20. The enhanced transport increases the lifetime of N20 because the photochemical lifetime is larger at high latitudes. 1