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Distributions of CO 2 and the mean age of stratospheric air are examined using the interactive two‐dimensional model described in the companion paper. It is shown that the model can explain the distribution of age in the lower stratosphere and reproduce the correlations between CO 2 and N 2 O observed at midlatitudes in the lower stratosphere. Seasonal characteristics of the measured correlations are captured by the model. The model uses externally specified coefficients K yy to account for large‐scale isentropic mixing in the stratosphere. The sensitivity of calculated distributions of CO 2 to K yy is be examined by comparing model runs using three different distributions of K yy . It is shown that the CO 2 measurements require K yy to exceed a threshold value of approximately 10 5 m 2 s −1 for most of the year. Once this threshold is exceeded, the slope of the CO 2 /N 2 correlations depends only weakly on the magnitude and the structure of the distribution of K yy .
Schneider et al. (Tue,) studied this question.