ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-13-8787-2013 Gravitational separation in the stratosphere – a new indicator of atmospheric circulation Ishidoya S. 1 Sugawara S. 2 Morimoto S. 3 Aoki S. 4 Nakazawa T. 4 Honda H. 5 Murayama S. 1 National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8569, Japan Miyagi University of Education, Sendai 980-0845, Japan National Institute of Polar Research, Tokyo 190-8518, Japan Center for Atmospheric and Oceanic Studies, Tohoku University, Sendai 980-8578, Japan Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara 252-5210, Japan 03 09 2013 13 17 8787 8796 Copyright: © 2013 S. Ishidoya et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/13/8787/2013/acp-13-8787-2013.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/13/8787/2013/acp-13-8787-2013.pdf

As a basic understanding of the dynamics of the atmospheric circulation, it has been believed that gravitational separation of atmospheric components is observable only in the atmosphere above the turbopause. However, we found, from our high-precision measurements of not only the isotopic ratios of N<sub>2</sub>, O<sub>2</sub> and Ar but also the mole fraction of Ar, that gravitational separation occurs even in the stratosphere below the turbopause; their observed vertical profiles are in good agreement with those expected theoretically from molecular mass differences. The O<sub>2</sub>/N<sub>2</sub> ratio observed in the middle stratosphere, corrected for gravitational separation, showed the same mean air age as estimated from the CO<sub>2</sub> mole fraction. Simulations with a 2-dimensional model of the middle atmosphere indicated that a relationship between gravitational separation and the age of air in the stratosphere would be significantly affected if the Brewer–Dobson circulation was enhanced due to global warming. Therefore, gravitational separation is usable as a new indicator of changes in the atmospheric circulation in the stratosphere.

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