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      Shift of subtropical transport barriers explains observed hemispheric asymmetry of decadal trends of age of air

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          Abstract

          In response to global warming, the Brewer–Dobson circulation in the stratosphere is expected to accelerate and the mean transport time of air along this circulation to decrease. This would imply a negative stratospheric age of air trend, i.e. an air parcel would need less time to travel from the tropopause to any point in the stratosphere. Age of air as inferred from tracer observations, however, shows zero to positive trends in the northern mid-latitude stratosphere and zonally asymmetric patterns. Using satellite observations and model calculations we show that the observed latitudinal and vertical patterns of the decadal changes of age of air in the lower to middle stratosphere during the period 2002–2012 are predominantly caused by a southward shift of the circulation pattern by about 5°. After correction for this shift, the observations reveal a hemispherically almost symmetric decrease of age of air in the lower to middle stratosphere up to 800 K of up to −0.25 years over the 2002–2012 period with strongest decrease in the northern tropics. This net change is consistent with long-term trends from model predictions.

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          Most cited references43

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          Acceleration of the Brewer–Dobson Circulation due to Increases in Greenhouse Gases

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            MIPAS: an instrument for atmospheric and climate research

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              Age of stratospheric air: Theory, observations, and models

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                Author and article information

                Journal
                Atmospheric Chemistry and Physics
                Atmos. Chem. Phys.
                Copernicus GmbH
                1680-7324
                2017
                September 21 2017
                : 17
                : 18
                : 11177-11192
                Article
                10.5194/acp-17-11177-2017
                400ed432-f940-4817-937f-f88015529b0b
                © 2017

                https://creativecommons.org/licenses/by/3.0/

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