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| Home > Publications database > Mixing and ageing in the polar lower stratosphere in winter 2015/2016 |
| Journal Article | FZJ-2018-00023 |
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2017
EGU
Katlenburg-Lindau
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Please use a persistent id in citations: http://hdl.handle.net/2128/16342 doi:10.5194/acp-2017-955
Abstract: We present data from winter 2015/2016, which were measured during the POLSTRACC (The Polar Stratosphere in a Changing Climate) aircraft campaign between December 2015 and March 2016. The focus of this work is on the role of transport and mixing between aged and potentially chemically processed air masses from the stratosphere with mid and low latitude air mass fractions with small transit times originating at the tropical lower stratosphere. By combining measurements of CO, N2O and SF6 we estimate the evolution of the relative contributions of transport and mixing to the UTLS composition over the course of the winter.We find an increasing influence of aged stratospheric air partly from the vortex as indicated by decreasing N2O and SF6 values over the course of winter. Surprisingly we also found a mean increase of CO by (3.00 ± 1.64) ppbV from January to March relative to N2O in the lower stratosphere. We show that this increase of CO is consistent with an increased mixing of tropospheric air as part of the fast transport mechanism in the lower stratosphere surf zone. The analysed air masses were partly affected by air masses which originated at the tropical tropopause and were quasi-horizontally mixed into higher latitudes.This increase of the tropospheric air fraction partly compensates for ageing of the UTLS due to the diabatic descent of air masses from the vortex by horizontally mixed, tropospheric influenced air masses. This is consistent with simulated age spectra from the Chemical Lagrangian Model of the Stratosphere (CLaMS), which show a respective fractional increase of tropospheric air with short transit times lower than six months and a simultaneous increase of aged air from deep stratospheric and vortex regions with transit times larger than two years.We thus conclude that the lowermost stratosphere in winter 2015/16 was affected by aged air from the deep stratosphere and vortex region. These air masses were significantly affected by increased mixing from the lower latitudes, which led to a simultaneous increase of the fraction of young air in the Arctic lowermost stratosphere over the course of winter.
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