Interpretation of high mixing ratios of O 3 observed in the upper troposphere over Syowa Station, Antarctica using a trajectory analysis

High O 3 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 O 3 was caused by vertical transport of O 3 from the lower stratosphere to the upper troposphere. To examine general features of the transport process associated with high O 3 mixing ratios observed in the upper troposphere over SYO, the same trajectory analysis was further performed for high O 3 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 O 3 over SYO, especially in spring and autumn, while the downward transport of stratospheric O 3 in the circumpolar region is important in summer.