Correction of stratospheric age of air (AoA) derived from sulfur hexafluoride (SF<sub>6</sub>) for the effect of chemical sinks
<p>Observational monitoring of the stratospheric transport circulation, the Brewer–Dobson circulation (BDC), is crucial to estimate any decadal to long-term changes therein, a prerequisite to interpret trends in stratospheric composition and to constrain the consequential impacts on climate. T...
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Copernicus Publications
2024-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/24/4193/2024/acp-24-4193-2024.pdf |
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| author | H. Garny H. Garny R. Eichinger R. Eichinger J. C. Laube E. A. Ray E. A. Ray G. P. Stiller H. Bönisch L. Saunders M. Linz |
| author_facet | H. Garny H. Garny R. Eichinger R. Eichinger J. C. Laube E. A. Ray E. A. Ray G. P. Stiller H. Bönisch L. Saunders M. Linz |
| author_sort | H. Garny |
| collection | DOAJ |
| description | <p>Observational monitoring of the stratospheric transport circulation, the Brewer–Dobson circulation (BDC), is crucial to estimate any decadal to long-term changes therein, a prerequisite to interpret trends in stratospheric composition and to constrain the consequential impacts on climate. The transport time along the BDC (i.e. the mean stratospheric age of air, AoA) can best be deduced from trace gas measurements of tracers which increase linearly with time and are chemically passive. The gas sulfur hexafluoride (SF<span class="inline-formula"><sub>6</sub></span>) is often used to deduce AoA because it has been increasing monotonically since the <span class="inline-formula">∼</span>1950s, and previously its chemical sinks in the mesosphere have been assumed to be negligible for AoA estimates. However, recent studies have shown that the chemical sinks of SF<span class="inline-formula"><sub>6</sub></span> are stronger than assumed and become increasingly relevant with rising SF<span class="inline-formula"><sub>6</sub></span> concentrations.</p>
<p>To adjust biases in AoA that result from the chemical SF<span class="inline-formula"><sub>6</sub></span> sinks, we here propose a simple correction scheme for SF<span class="inline-formula"><sub>6</sub></span>-based AoA estimates accounting for the time-dependent effects of chemical sinks. The correction scheme is based on theoretical considerations with idealized assumptions, resulting in a relation between ideal AoA and apparent AoA which is a function of the tropospheric reference time series of SF<span class="inline-formula"><sub>6</sub></span> and of the AoA-dependent effective lifetime of SF<span class="inline-formula"><sub>6</sub></span>. The correction method is thoroughly tested within a self-consistent data set from a climate model that includes explicit calculation of chemical SF<span class="inline-formula"><sub>6</sub></span> sinks. It is shown within the model that the correction successfully reduces biases in SF<span class="inline-formula"><sub>6</sub></span>-based AoA to less than 5 % for mean ages below 5 years. Tests using only subsampled data for deriving the fit coefficients show that applying the correction scheme even with imperfect knowledge of the sink is far superior to not applying a sink correction.</p>
<p><span id="page4194"/>Furthermore, we show that based on currently available measurements, we are not able to constrain the fit parameters of the correction scheme based on observational data alone. However, the model-based correction curve lies within the observational uncertainty, and we thus recommend using the model-derived fit coefficients until more high-quality measurements are able to further constrain the correction scheme. The application of the correction scheme to AoA from satellites and in situ data suggests that it is highly beneficial to reconcile different observational estimates of mean AoA.</p> |
| first_indexed | 2024-04-24T11:46:43Z |
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| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-24T11:46:43Z |
| publishDate | 2024-04-01 |
| publisher | Copernicus Publications |
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| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-38a5b59debb04d6089533ac994852a0c2024-04-09T10:00:04ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242024-04-01244193421510.5194/acp-24-4193-2024Correction of stratospheric age of air (AoA) derived from sulfur hexafluoride (SF<sub>6</sub>) for the effect of chemical sinksH. Garny0H. Garny1R. Eichinger2R. Eichinger3J. C. Laube4E. A. Ray5E. A. Ray6G. P. Stiller7H. Bönisch8L. Saunders9M. Linz10Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, GermanyMeteorological Institute, Ludwig-Maximilians-Universität München, Munich, GermanyDeutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, GermanyDepartment of Atmospheric Physics, Faculty of Mathematics and Physics, Charles University Prague, Prague, Czech RepublicInstitut für Energie- und Klimaforschung (IEK-7), Forschungszentrum Jülich GmbH, Jülich, GermanyChemical Sciences Division, Earth Systems Research Laboratory, NOAA, Boulder, Colorado, USACooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USAInstitute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, GermanyInstitute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, GermanyDepartment of Physics, University of Toronto, Toronto, Ontario, CanadaDepartment of Earth and Planetary Sciences, School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA<p>Observational monitoring of the stratospheric transport circulation, the Brewer–Dobson circulation (BDC), is crucial to estimate any decadal to long-term changes therein, a prerequisite to interpret trends in stratospheric composition and to constrain the consequential impacts on climate. The transport time along the BDC (i.e. the mean stratospheric age of air, AoA) can best be deduced from trace gas measurements of tracers which increase linearly with time and are chemically passive. The gas sulfur hexafluoride (SF<span class="inline-formula"><sub>6</sub></span>) is often used to deduce AoA because it has been increasing monotonically since the <span class="inline-formula">∼</span>1950s, and previously its chemical sinks in the mesosphere have been assumed to be negligible for AoA estimates. However, recent studies have shown that the chemical sinks of SF<span class="inline-formula"><sub>6</sub></span> are stronger than assumed and become increasingly relevant with rising SF<span class="inline-formula"><sub>6</sub></span> concentrations.</p> <p>To adjust biases in AoA that result from the chemical SF<span class="inline-formula"><sub>6</sub></span> sinks, we here propose a simple correction scheme for SF<span class="inline-formula"><sub>6</sub></span>-based AoA estimates accounting for the time-dependent effects of chemical sinks. The correction scheme is based on theoretical considerations with idealized assumptions, resulting in a relation between ideal AoA and apparent AoA which is a function of the tropospheric reference time series of SF<span class="inline-formula"><sub>6</sub></span> and of the AoA-dependent effective lifetime of SF<span class="inline-formula"><sub>6</sub></span>. The correction method is thoroughly tested within a self-consistent data set from a climate model that includes explicit calculation of chemical SF<span class="inline-formula"><sub>6</sub></span> sinks. It is shown within the model that the correction successfully reduces biases in SF<span class="inline-formula"><sub>6</sub></span>-based AoA to less than 5 % for mean ages below 5 years. Tests using only subsampled data for deriving the fit coefficients show that applying the correction scheme even with imperfect knowledge of the sink is far superior to not applying a sink correction.</p> <p><span id="page4194"/>Furthermore, we show that based on currently available measurements, we are not able to constrain the fit parameters of the correction scheme based on observational data alone. However, the model-based correction curve lies within the observational uncertainty, and we thus recommend using the model-derived fit coefficients until more high-quality measurements are able to further constrain the correction scheme. The application of the correction scheme to AoA from satellites and in situ data suggests that it is highly beneficial to reconcile different observational estimates of mean AoA.</p>https://acp.copernicus.org/articles/24/4193/2024/acp-24-4193-2024.pdf |
| spellingShingle | H. Garny H. Garny R. Eichinger R. Eichinger J. C. Laube E. A. Ray E. A. Ray G. P. Stiller H. Bönisch L. Saunders M. Linz Correction of stratospheric age of air (AoA) derived from sulfur hexafluoride (SF<sub>6</sub>) for the effect of chemical sinks Atmospheric Chemistry and Physics |
| title | Correction of stratospheric age of air (AoA) derived from sulfur hexafluoride (SF<sub>6</sub>) for the effect of chemical sinks |
| title_full | Correction of stratospheric age of air (AoA) derived from sulfur hexafluoride (SF<sub>6</sub>) for the effect of chemical sinks |
| title_fullStr | Correction of stratospheric age of air (AoA) derived from sulfur hexafluoride (SF<sub>6</sub>) for the effect of chemical sinks |
| title_full_unstemmed | Correction of stratospheric age of air (AoA) derived from sulfur hexafluoride (SF<sub>6</sub>) for the effect of chemical sinks |
| title_short | Correction of stratospheric age of air (AoA) derived from sulfur hexafluoride (SF<sub>6</sub>) for the effect of chemical sinks |
| title_sort | correction of stratospheric age of air aoa derived from sulfur hexafluoride sf sub 6 sub for the effect of chemical sinks |
| url | https://acp.copernicus.org/articles/24/4193/2024/acp-24-4193-2024.pdf |
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