Detecting multi-decadal changes in the Brewer-Dobson circulation from in situ trace gas measurements and idealized modeling

We utilize in situ stratospheric measurements of trace gases from two recent high altitude aircraft campaigns, DCOTTS and SABRE, to compare mean ages and long-lived trace gas relationships in the NH stratosphere to those from ER-2 campaigns in the 1990s.  The ER-2 campaign data from three decades ago have been a primary reference for in situ-based estimates of mean age in the lower stratosphere from 16-22 km altitude, but very few measurements have been made in this region since then.  We use an updated technique to consistently calculate mean ages from simultaneous in situ measurements of SF₆, CO₂, N₂O and CH₄, allowing us to compare mean ages and their relationship with N₂O between the 1990s and 2020s.  The mesospheric loss of SF₆ and subsequent old age biases are largely accounted for based on newly developed theory and modeling work.  We then use the idealized tropical leaky pipe model to explore stratospheric circulation and mixing changes that are consistent with the observations.