Interpretation of high mixing ratios of O₃ observed in the upper troposphere over Syowa Station, Antarctica using a trajectory analysis

High O₃ mixing ratios were observed above 6 km over Syowa Station (SYO), Antarctica in mid-September 1989 when the tropopause was found to be higher than 10 km. From the results of a 3-dimensional trajectory analysis, it is suggested that the observed high O₃ was caused by vertical transport of O₃ from the lower stratosphere to the upper troposphere. To examine general features of the transport process associated with high O₃ mixing ratios observed in the upper troposphere over SYO, the same trajectory analysis was further performed for high O₃ observations at 350 hPa over SYO in 1987-1994. The results imply that the transport of stratospheric air descending in the polar region to SYO plays a very important role in the increase of upper tropospheric O₃ over SYO, especially in spring and autumn, while the downward transport of stratospheric O₃ in the circumpolar region is important in summer.