Mean Stratospheric Age of Air from Satellite Observations of N2O and Tracer Correlations

Climate modeling studies predict a strengthening of the Brewer Dobson Circulation, which has implications for global atmospheric composition, radiation, and climate. This predicted acceleration has not been confirmed with observations, and models also disagree about the mean stratospheric circulation and mixing strength. In previous work, we developed a long record of mean age of air from an N2O combined satellite product – part of the Stratospheric Water and OzOne Satellite Homogenized (SWOOSH) package – by inferring age from latitude-dependent Age:N2O relationships. While SWOOSH corrects for the drift in Microwave Limb Sounder (MLS) N2O measurements, positive trends in derived mean ages over the past two decades based on these fixed Age:N2O relationships are in contrast to mean age trends derived from Atmospheric Chemistry Experiment (ACE) SF6 and in situ measurements. This contrast in mean age trends confirms the changes of the in-situ Age:N2O relationship over time and indicates a need to have both latitude and time varying Age:N2O relationships for more accurate age derivations. Using time-varying Age:N2O relationships, we introduce an N2O-derived mean age product that now addresses 1) biases in satellite N2O observations and 2) the positive N2O-age trends. In addition, we compare our results with previous mean age trend analyses to determine if the corrections are robust, which will further contribute to understanding long-term circulation and mixing variability based on observed trace gas trends.