Journal Article

FZJ-2022-03424

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Hemispheric asymmetries in recent changes in the stratospheric circulation

Ploeger, F. (Corresponding author)FZJ* ; Garny, H.FZJ*

2022
EGU Katlenburg-Lindau

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Please use a persistent id in citations: http://hdl.handle.net/2128/31871  doi:10.5194/acp-22-5559-2022

Abstract: The expected effect of ozone recovery on the stratospheric Brewer–Dobson circulation (BDC) is a slow-down, strongest in the Southern Hemisphere (SH). In contrast, the BDC has been found to weaken more strongly in the Northern Hemisphere (NH) relative to the SH in recent decades, inducing substantial effects on chemical composition. We investigate hemispheric asymmetries in BDC changes since about 2000 in simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven with different reanalyses (ERA5, ERA-Interim, JRA-55, MERRA-2) and contrast those to free-running climate model simulations. We find that age-of-air increases robustly in the NH stratosphere relative to the SH in all reanalyses. Related nitrous oxide changes agree well between reanalysis-driven simulations and satellite measurements, providing observational evidence for the hemispheric asymmetry in BDC changes. We show that the composition changes in reanalyses are caused by structural residual-circulation changes related to an upward shift and strengthening of the deep BDC branch, resulting in longer transit times, and a downward shift and weakening shallow branch in the NH relative to the SH. Although climate model simulations show that ozone recovery will lead to overall reduced circulation and age-of-air trends, the hemispherically asymmetric signal in circulation trends is small compared to internal variability. Therefore, observed circulation trends over the recent past are not in contradiction to expectations from climate models. Furthermore, the hemispheric asymmetry in BDC trends imprints on the composition of the lower stratosphere, and the signal might propagate into the troposphere, potentially affecting composition down to the surface.

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Contributing Institute(s):

1. Stratosphäre (IEK-7)

Research Program(s):

1. 2112 - Climate Feedbacks (POF4-211) (POF4-211)
2. 2B3 - ESM (CTA - CCA) (POF4-2B3) (POF4-2B3)
3. DFG project 428312742 - TRR 301: Die Tropopausenregion in einer Atmosphäre im Wandel (428312742)

Appears in the scientific report 2022

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