To examine gravitational separation of the stratospheric air over Antarctica in austral summer, we collected air samples from altitudes of 10 to 30 km over Syowa Station (69.0°S, 39.6°E) using balloon-borne cryogenic samplers for the period 1998–2013, and then analyzed them for δ15N of N2, δ18O of O2, δ(Ar/N2) and δ40Ar. The normalized mass ratio “δ,” calculated using their measured values, decreases with increasing altitude, implying an upward enhancement of the gravitational separation effect. The observed stratospheric δ profiles are generally well reproduced by a two-dimensional atmospheric model, but the model tends to underestimate the observed δ values in the middle stratosphere above 26 km. We also observe interannual variation in the δ vertical profile in the middle stratosphere. A backward trajectory analysis suggests that this variation is attributable to different horizontal mixing of the stratospheric air over Antarctica from year to year.
- Balloon-borne cryogenic air sampler
- Gravitational separation of the atmosphere
- Meteorological field
- Stratosphere over Antarctica