Title: Changing width of the Lagrangian Cold-point Tropopause
Susann Tegtmeier (Institute of Space and Atmospheric Studies, University of Saskatchewan, Canada)
Abstract:
The tropical tropopause layer (TTL) serves as a crucial boundary for air exchange between the troposphere and stratosphere, influencing the chemical composition and radiative balance of the region. Specifically, the cold-point tropopause, where air parcels undergo final dehydration, plays a key role in determining stratospheric water vapor content, which has significant implications for the global energy budget.
Here, we use 44 years (1981–2024) of Lagrangian trajectory simulations to quantify long-term changes in the temperature and meridional width of the Lagrangian cold-point (LCP) region. We introduce a trajectory- based metric, defined as the 90th-percentile latitude range containing the majority of LCPs, to diagnose the spatial extent of stratospheric entry pathways. We find statistically significant cooling of LCP temperatures and a narrowing of the LCP width (−0.35±0.10° per decade). The latter is consistent with a narrowing of the Intertropical Convergence Zone (ITCZ) in the troposphere. These results provide strong evidence that stratospheric entry pathways have become increasingly confined over recent decades, with implications for TTL dehydration and lower-stratospheric water vapor trends.
Bio:
Prof. Tegtmeier’s research in the field of atmospheric chemistry-climate interactions is focused on the role of middle atmosphere transport and composition. Her work is based on the use of models and observational data sets, resulting in interdisciplinary research investigating physical and chemical processes from the Earth’s surface up to the stratosphere. She is co-chair of the World Climate Research Programme (WCRP) core project on Earth System Modelling and Observations (ESMO) and was a lead author of the UNEP/WMO Scientific Assessment of Ozone Depletion: 2022. Her research has provided new insights into the chemical aspects of ocean-middle atmosphere coupling by quantifying the impact of anthropogenic activities on oceanic halocarbon production. Another aspect of her research focuses on long-term changes and variability of stratospheric temperature, ozone, water vapour and other trace gases from satellite observations, reanalyses and model simulations.
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