Climate models predict that the Brewer-Dobson Circulation (BDC) will accelerate due to the warming atmosphere. This would increase trace gas transportation from the tropics to higher latitudes and result in further changes to the radiative properties of the atmosphere, creating a feedback effect. Stratospheric age of air can be used to determine whether this acceleration is occurring. Age of air is defined as the time that has elapsed since a stratospheric air parcel left the troposphere. It is a useful diagnostic for atmospheric transport: air that is too young at higher latitudes indicates rapid transport, while old air indicates slow transport. Changes in age of air can therefore signal changes in the BDC. Detecting such changes requires a long-term observational record of age of air, which until now has been difficult to obtain due to low availability of measurements. The trace gas SF6 provides a reliable way to calculate age of air, but it is difficult to measure due to its small concentrations. The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) provides the longest available record of SF6, spanning 2004 to the present. In this talk, I will discuss how monthly age of air is calculated using ACE-FTS SF6 measurements and show comparisons with the existing observation-based age of air datasets. The results are promising, indicating that the new ACE-based age of air dataset can likely be used to detect whether there is a significant trend in stratospheric age of air.
Host: Ramina Alwarda