Seasonal changes of air parcel's trajectories arriving at the Japan Area

As the economies of Eastern Asia have drastically grown in recent years, a large amount of air pollutants is supplied from Eastern Asia to the atmosphere. The anthropogenic and natural materials such as gas, aerosol, and dust are widely distributed with the interannual and seasonal variability. Examining the role of atmospheric circulation in mass transport in Eastern Asia, air parcel’s trajectories arriving at Japan Area are investigated. In this study, air parcel’s trajectories were calculated using wind fields in sigma coordinate. We used grid point values of geopotential height and wind component from the NCEP/DOE AMIP-II reanalysis data. The 7-day backward air parcel’s trajectories arriving at Kyushu (32.5N, 131.0E) and Hokkaido (43.5N, 142.5E) regions in boundary layer were calculated from January 1999 to December 2001.

The source and transport pathway of air parcels arriving at Kyushu and Hokkaido regions for one year were widely distributed over Eurasia and Pacific Ocean, and the seasonal variability occurred. Although the Kyushu region is close to the Hokkaido region from a point view of global scale, the source and transport pathway of air parcels arriving at those area were greatly different. It was also found out that the passage of troughs played an important role in transport of middle tropospheric air parcels over the Asian continent toward the lower troposphere on the mid-latitude coastal region of the Asian continent. It was suggested that the seasonal variability of Pacific and continental high pressure systems contributed to the seasonal features of air parcel’s trajectories arriving at the Japan Area.