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<p>The Brewer–Dobson circulation largely determines the distribution of key trace gases and aerosols in the stratosphere and is projected to accelerate under climate change in chemistry-climate models simulations. However, observational constraints based on the mean age of air have suggested weak increases, implying a possible slowdown of the circulation and a discrepancy from model projections. Here we examine changes in the strength of the Northern Hemisphere stratospheric circulation over 1993–2025 by reanalysing mean age of air from existing and new in situ measurements. We identify differences across sampling systems and apply improved data processing to produce a more reliable observational record. Our revised estimates show negative trends in Northern Hemisphere extratropical mean age—opposite in sign to most earlier studies—and indicative of an acceleration of the stratospheric circulation since the 1990s, in line with model expectations. However, the observed acceleration is stronger than simulated and exhibits a different vertical structure. These results reduce the apparent gap between observations and models but also point to remaining discrepancies, highlighting the need for improved measurement practices and refined model representations of stratospheric circulation.</p>

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Observed stratospheric mean age decrease consistent with circulation acceleration

  • 期刊论文

  • 发表日期：

    2026年6月16日

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  • Eric A. Ray,
  • Bianca C. Baier,
  • Fred L. Moore,
  • Hella Garny,
  • Markus Jesswein,
  • Jianghanyang Li,
  • Eric J. Hintsa,
  • Bradley D. Hall,
  • Geoff S. Dutton,
  • David Nance,
  • Colm Sweeney,
  • Sean M. Davis,
  • Béatrice Josse,
  • Olaf Morgenstern,
  • Patrick Jöckel,
  • David Plummer

摘要

The Brewer–Dobson circulation largely determines the distribution of key trace gases and aerosols in the stratosphere and is projected to accelerate under climate change in chemistry-climate models simulations. However, observational constraints based on the mean age of air have suggested weak increases, implying a possible slowdown of the circulation and a discrepancy from model projections. Here we examine changes in the strength of the Northern Hemisphere stratospheric circulation over 1993–2025 by reanalysing mean age of air from existing and new in situ measurements. We identify differences across sampling systems and apply improved data processing to produce a more reliable observational record. Our revised estimates show negative trends in Northern Hemisphere extratropical mean age—opposite in sign to most earlier studies—and indicative of an acceleration of the stratospheric circulation since the 1990s, in line with model expectations. However, the observed acceleration is stronger than simulated and exhibits a different vertical structure. These results reduce the apparent gap between observations and models but also point to remaining discrepancies, highlighting the need for improved measurement practices and refined model representations of stratospheric circulation.