1National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8569, Japan
2Miyagi University of Education, Sendai 980-0845, Japan
3National Institute of Polar Research, Tokyo 190-8518, Japan
4Center for Atmospheric and Oceanic Studies, Tohoku University, Sendai 980-8578, Japan
5Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara 252-5210, Japan
Abstract. 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 N2, O2 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 O2/N2 ratio observed in the middle stratosphere, corrected for gravitational separation, showed the same mean air age as estimated from the CO2 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.