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Cosmogenic 35S Tracer Evidence for Seasonal Stratosphere‐to‐troposphere Transport Over the Southeastern Tibetan Plateau.

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Title: Cosmogenic 35S Tracer Evidence for Seasonal Stratosphere‐to‐troposphere Transport Over the Southeastern Tibetan Plateau.
Authors: Liu, Yixi1,2,3 (AUTHOR), Kang, Shichang1,4,5 (AUTHOR), Wang, Kun1 (AUTHOR), Lin, Xiaomin4,6 (AUTHOR), Zhang, Chao1,4 (AUTHOR), Yan, Fangping1 (AUTHOR), Pu, Tao1,4 (AUTHOR), Wang, Pengling7 (AUTHOR), Li, Chaoliu1,8 (AUTHOR) lichaoliuli@126.com, Lin, Mang6 (AUTHOR) linm@gig.ac.cn
Source: Journal of Geophysical Research. Atmospheres. 6/28/2026, Vol. 131 Issue 12, p1-15. 15p.
Subject Terms: *Radioactive tracers, *Atmospheric chemistry, *Radiative forcing, *Atmospheric aerosols, Atmospheric transport, Tracers (Chemistry), Seasons
Geographic Terms: Tibet (China)
Abstract: Stratosphere‐to‐troposphere transport (STT) is a key process that influences atmospheric chemical composition and radiative balance. The Tibetan Plateau (TP), the highest and most extensive plateau in the world, has been identified as a global hotspot for stratospheric intrusions. However, direct observational evidence remains limited, particularly in the southeastern TP—a region traditionally considered to have minimal STT influence. Stratospheric 35S is a powerful tracer for directly identifying STT processes. Here, we present the first measurements of 35SO42− concentrations and their seasonal variability in aerosols collected at Yaze, a remote site in the southeastern TP. The highest 35S activity (840 ± 90 atoms m−3) occurred in spring and coincided with elevated surface ozone levels. Backward trajectory and vertical motion analyses indicate that this spring enhancement was attributable to descending stratospheric air masses originating from the Himalayan region, highlighting the prominent influence of frequent STT events during this season. A secondary 35S activity peak in November (810 ± 80 atoms m−3) was associated with stratospheric intrusions from the northwestern TP. These findings provide direct observational evidence of pronounced seasonal variability in stratospheric intrusions over the southeastern TP and enhance our understanding of regional stratosphere–troposphere exchange processes. Furthermore, we report 35SO42− concentrations measured in spring glacier snowpits and summer precipitation from the nearby glaciers, which are associated with atmospheric 35SO42− and serve as representative end‐member values for glacier runoff, establishing essential baseline data for future assessments of glacier melt and hydrological responses in this climatically sensitive region. Plain Language Summary: Stratospheric components such as ozone can enter the troposphere, influencing atmospheric oxidizing power, the formation of secondary aerosols, and atmospheric radiative forcing. However, STT in the southeastern TP— a critical region facilitating the exchange of air between the Tibetan Plateau and South Asia—has been rarely investigated. In this study, we use the cosmogenic tracer 35S to track the seasonal pattern of stratospheric intrusion in this important region. After being deposited from the atmosphere into surface snow or water, the activity of 35S decreases continuously through radioactive decay. We measured 35SO42− concentrations in spring glacier snow and monsoon‐season precipitation in the southeastern TP to quantify their relationship with atmospheric measurements. These results not only provide clear evidence of springtime stratospheric air‐mass intrusions but also offer a potential tool for tracing glacial meltwater movement in future studies. Key Points: Seasonal pattern of 35SO42− in aerosols in the southeastern Tibetan Plateau is firstly investigatedHigh 35SO42− concentrations in April and November directly indicate stratospheric intrusion35SO42− concentrations in spring glacier snowpits and monsoon rainwater provide us with new insight in glacial melting [ABSTRACT FROM AUTHOR]
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Description
Abstract:Stratosphere‐to‐troposphere transport (STT) is a key process that influences atmospheric chemical composition and radiative balance. The Tibetan Plateau (TP), the highest and most extensive plateau in the world, has been identified as a global hotspot for stratospheric intrusions. However, direct observational evidence remains limited, particularly in the southeastern TP—a region traditionally considered to have minimal STT influence. Stratospheric 35S is a powerful tracer for directly identifying STT processes. Here, we present the first measurements of 35SO42− concentrations and their seasonal variability in aerosols collected at Yaze, a remote site in the southeastern TP. The highest 35S activity (840 ± 90 atoms m−3) occurred in spring and coincided with elevated surface ozone levels. Backward trajectory and vertical motion analyses indicate that this spring enhancement was attributable to descending stratospheric air masses originating from the Himalayan region, highlighting the prominent influence of frequent STT events during this season. A secondary 35S activity peak in November (810 ± 80 atoms m−3) was associated with stratospheric intrusions from the northwestern TP. These findings provide direct observational evidence of pronounced seasonal variability in stratospheric intrusions over the southeastern TP and enhance our understanding of regional stratosphere–troposphere exchange processes. Furthermore, we report 35SO42− concentrations measured in spring glacier snowpits and summer precipitation from the nearby glaciers, which are associated with atmospheric 35SO42− and serve as representative end‐member values for glacier runoff, establishing essential baseline data for future assessments of glacier melt and hydrological responses in this climatically sensitive region. Plain Language Summary: Stratospheric components such as ozone can enter the troposphere, influencing atmospheric oxidizing power, the formation of secondary aerosols, and atmospheric radiative forcing. However, STT in the southeastern TP— a critical region facilitating the exchange of air between the Tibetan Plateau and South Asia—has been rarely investigated. In this study, we use the cosmogenic tracer 35S to track the seasonal pattern of stratospheric intrusion in this important region. After being deposited from the atmosphere into surface snow or water, the activity of 35S decreases continuously through radioactive decay. We measured 35SO42− concentrations in spring glacier snow and monsoon‐season precipitation in the southeastern TP to quantify their relationship with atmospheric measurements. These results not only provide clear evidence of springtime stratospheric air‐mass intrusions but also offer a potential tool for tracing glacial meltwater movement in future studies. Key Points: Seasonal pattern of 35SO42− in aerosols in the southeastern Tibetan Plateau is firstly investigatedHigh 35SO42− concentrations in April and November directly indicate stratospheric intrusion35SO42− concentrations in spring glacier snowpits and monsoon rainwater provide us with new insight in glacial melting [ABSTRACT FROM AUTHOR]
ISSN:2169897X
DOI:10.1029/2025JD046026