Analysis of residual mean transport in the stratosphere: 2. Distributions of CO2 and mean age

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Abstract
Distributions of CO2 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 CO2 and N2O observed at midlatitudes in the lower stratosphere. Seasonal characteristics of the measured correlations are captured by the model. The model uses externally specified coefficients Kyy to account for large‐scale isentropic mixing in the stratosphere. The sensitivity of calculated distributions of CO2 to Kyy is be examined by comparing model runs using three different distributions of Kyy. It is shown that the CO2 measurements require Kyy to exceed a threshold value of approximately 105 m2 s−1 for most of the year. Once this threshold is exceeded, the slope of the CO2/N2 correlations depends only weakly on the magnitude and the structure of the distribution of Kyy.