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 the 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 concentration of Ar, that the 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 the gravitational separation, showed the same mean air age as estimated from the CO2 concentration. Simulations with a 2-dimensional model of the middle atmosphere indicated that a relationship between the gravitational separation and the air age in the stratosphere would be significantly affected if the Brewer-Dobson circulation is enhanced due to global warming. Therefore, the gravitational separation is usable as a new indicator of changes in the atmospheric circulation in the stratosphere.