Preprints
https://doi.org/10.5194/egusphere-2025-4457
https://doi.org/10.5194/egusphere-2025-4457
01 Oct 2025
 | 01 Oct 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Tropical upwelling as seen in observations of the tape recorder signal

Meghan Brehon, Susann Tegtmeier, Adam Bourassa, Sean M. Davis, Udo Grabowski, Tobias Kerzenmacher, and Gabriele Stiller

Abstract. Tropical upwelling constitutes the ascending branch of the global mean stratospheric circulation and governs the thermal and chemical properties of the tropical stratosphere. A lack of direct observations and a spread in upwelling structure across the modern reanalysis creates difficulties in determining variability and long-term changes of tropical upwelling. We have derived time series of effective vertical transport in the tropical lower and middle stratosphere from MLS and SWOOSH water vapour for 2005–2020 and 1995–2020. Our calculated upwelling is found to be in the range of 0.21–0.33 mm/s for 73–28 hPa in very good agreement with reanalysis vertical velocities (ERA5, JRA-3Q, MERRA-2) and other observation-based estimates (ANCISTRUS).

We show that interannual variations of upwelling in the middle stratosphere are dominated by the QBO signal, which explains a large fraction of the upwelling anomalies. In the lower stratosphere, tropospheric modes of variability also play a role with the QBO and ENSO being equally important for explaining interannual variability. Individual peaks of strongly enhanced upwelling in the lower stratosphere in 2000/2001 and 2011/2012 cannot be explained by QBO or ENSO variability and coincide with known drops in water vapour and cold point temperatures. We use independent observational data to show that tropical upwelling is anticorrelated with long-lived tracers such as ozone as expected, lending confidence to the derived values. A reduction in variability is observed for 2016–2020 in both our calculated upwelling and observed ozone, which is consistent with the disruption to regular QBO variability over this period.

Competing interests: One author is a member of the editorial board of ACP.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Meghan Brehon, Susann Tegtmeier, Adam Bourassa, Sean M. Davis, Udo Grabowski, Tobias Kerzenmacher, and Gabriele Stiller

Status: open (until 12 Nov 2025)

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Meghan Brehon, Susann Tegtmeier, Adam Bourassa, Sean M. Davis, Udo Grabowski, Tobias Kerzenmacher, and Gabriele Stiller
Meghan Brehon, Susann Tegtmeier, Adam Bourassa, Sean M. Davis, Udo Grabowski, Tobias Kerzenmacher, and Gabriele Stiller
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Latest update: 01 Oct 2025
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Short summary
We used satellite-based water vapour data to estimate vertical transport rates in the tropical stratosphere for 1995 to 2020. These estimates were compared with other upwelling datasets and used to analyze stratospheric variability. Our results find good agreement between the datasets and reveal that variability in upwelling is mainly driven by known climate patterns like the QBO and ENSO with a clear signal in the upwelling time series coinciding with the QBO disruptions of 2015/16 and 2019/20.
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