Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 10195-10213, 2016
http://www.atmos-chem-phys.net/16/10195/2016/
doi:10.5194/acp-16-10195-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
11 Aug 2016
Seasonal and inter-annual variability of lower stratospheric age of air spectra
Felix Ploeger1 and Thomas Birner2 1Institute for Energy and Climate Research: Stratosphere (IEK–7), Forschungszentrum Jülich, Jülich, Germany
2Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA
Abstract. Trace gas transport in the lower stratosphere is investigated by analysing seasonal and inter-annual variations of the age of air spectrum – the probability distribution of stratospheric transit times. Age spectra are obtained using the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by ERA-Interim winds and total diabatic heating rates, and using a time-evolving boundary-impulse-response (BIER) method based on multiple tracer pulses. Seasonal age spectra show large deviations from an idealized stationary uni-modal shape. Multiple modes emerge in the spectrum throughout the stratosphere, strongest at high latitudes, caused by the interplay of seasonally varying tropical upward mass flux, stratospheric transport barriers and recirculation. Inter-annual variations in transport (e.g. quasi-biennial oscillation) cause significant modulations of the age spectrum shape. In fact, one particular QBO phase may determine the spectrum's mode during the following 2–3 years. Interpretation of the age spectrum in terms of transport contributions due to the residual circulation and mixing is generally not straightforward. It turns out that advection by the residual circulation represents the dominant pathway in the deep tropics and in the winter hemisphere extratropics above 500 K, controlling the modal age in these regions. In contrast, in the summer hemisphere, particularly in the lowermost stratosphere, mixing represents the most probable pathway controlling the modal age.

Citation: Ploeger, F. and Birner, T.: Seasonal and inter-annual variability of lower stratospheric age of air spectra, Atmos. Chem. Phys., 16, 10195-10213, doi:10.5194/acp-16-10195-2016, 2016.
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Short summary
We investigate the aging of air in the stratosphere caused by transport due to Brewer's circulation, using the Boundary Impulse Evolving Response (BIER) method. The age spectra show multiple peaks caused by the seasonal and inter-annual variations of transport. The modal age is controlled by the residual circulation in the tropics and winter hemisphere extratropics and by mixing in the summer hemisphere. Analysis of the full age spectrum is strongly recommended for model inter-comparisons.
We investigate the aging of air in the stratosphere caused by transport due to Brewer's...
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