Quantifying transport into the lowermost stratosphere using simultaneous in-situ measurements of SF6 and CO2
Open Access
- 19 August 2009
- journal article
- Published by Copernicus GmbH in Atmospheric Chemistry and Physics
- Vol. 9 (16), 5905-5919
- https://doi.org/10.5194/acp-9-5905-2009
Abstract
The seasonality of transport and mixing of air into the lowermost stratosphere (LMS) is studied using distributions of mean age of air and a mass balance approach, based on in-situ observations of SF6 and CO2 during the SPURT (Spurenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region) aircraft campaigns. Combining the information of the mean age of air and the water vapour distributions we demonstrate that the tropospheric air transported into the LMS above the extratropical tropopause layer (ExTL) originates predominantly from the tropical tropopause layer (TTL). The concept of our mass balance is based on simultaneous measurements of the two passive tracers and the assumption that transport into the LMS can be described by age spectra which are superposition of two different modes. Based on this concept we conclude that the stratospheric influence on LMS composition is strongest in April with extreme values of the tropospheric fractions (α1) below 20% and that the strongest tropospheric signatures are found in October with α1 greater than 80%. Beyond the fractions, our mass balance concept allows us to calculate the associated transit times for transport of tropospheric air from the tropics into the LMS. The shortest transit times (<0.3 years) are derived for the summer, continuously increasing up to 0.8 years by the end of spring. These findings suggest that strong quasi-horizontal mixing across the weak subtropical jet from summer to mid of autumn and the considerably shorter residual transport time-scales within the lower branch of the Brewer-Dobson circulation in summer than in winter dominates the tropospheric influence in the LMS until the beginning of next year's summer.Keywords
This publication has 66 references indexed in Scilit:
- Characterization of the composition, structure, and seasonal variation of the mixing layer above the extratropical tropopause as revealed by MOZAIC measurementsJournal of Geophysical Research: Atmospheres, 2008
- Model evaluation of CO2 and SF6 in the extratropical UT/LS regionJournal of Geophysical Research: Atmospheres, 2008
- A Lagrangian perspective of the tropopause and the ventilation of the lowermost stratosphereJournal of Geophysical Research: Atmospheres, 2007
- Fine‐scale structure of the extratropical tropopause regionJournal of Geophysical Research: Solid Earth, 2006
- Empirical age spectra for the midlatitude lower stratosphere from in situ observations of CO2: Quantitative evidence for a subtropical “barrier” to horizontal transportJournal of Geophysical Research: Atmospheres, 2001
- Empirical age spectra for the lower tropical stratosphere from in situ observations of CO2: Implications for stratospheric transportJournal of Geophysical Research: Atmospheres, 1999
- Stratospheric Mean Ages and Transport Rates from Observations of Carbon Dioxide and Nitrous OxideScience, 1996
- Seasonal variation of mass transport across the tropopauseJournal of Geophysical Research: Solid Earth, 1996
- Isentropic cross‐tropopause mass exchange in the extratropicsJournal of Geophysical Research: Atmospheres, 1995
- Tracer‐tracer relationships and lower stratospheric dynamics: CO2 and N2O correlations during SPADEGeophysical Research Letters, 1994