Vertical distribution of the tropospheric ozone over Japan: The origin of the ozone peaks

Vertical distributions of the tropospheric ozone over Wakasa Bay, Enshu-nada and some other places in Japan were measured by a series of aircraft measurements during 1987-1991. The backward trajectories of air parcels with the ozone peaks and potential vorticity distributions around them were then analyzed to study their origin. This result showed that the ozone peaks over Japan sometimes originated from the tropopause folding which occurred in the west of Japan. Two ozone peaks had different altitudes and concentrations over Enshu-nada on 21 January 1989 which originated from different tropopause foldings. They seemed to diffuse during the transport which resulted in a stratified structure forming over Japan. The two similar ozone peaks, which originated from the identical tropopause folding and were observed 300 km away on 21 January 1989, belonged to the identical ozone layer based on the potential temperature inclination. Two different types of air masses were simultaneously observed at different points over Japan on 8 August 1990. One was the continental air mass which showed a high ozone and a low water vapor concentration being transported from the northeast of China. The other was the maritime air mass which showed a low ozone and a high water vapor concentration staying over the sea for a few days that didn't come across the stratospheric air mass and pass over the metropolitan area. However, the ozone and water vapor showed a positive correlation even when the maritime air mass passed over the metropolitan or industrial areas, thus showing that the concentrations of the ozone and vapor were both high. The vertical distribution of ozone on 27 April 1991 over Tsukuba was almost uniform and the concentration was approximately 70 ppbv. This suggested that the air masses came from the folding area whose vertical inclination of potential vorticity was small and was transported shortly after this event. Not only intrusion from the stratosphere but diffusion during the transport was also important for the ozone distribution over Japan based on the relationship between the concentration of ozone and the distance of transport.