MEASUREMENTS OF ATMOSPHERIC CO2 AND CH4 USING A COMMERCIAL AIRLINER FROM 1993 TO 1994

A new automatic flask sampling system for the Boeing 747 commercial ai rliner was developed to observe CO2 and CH4 mixing ratios in the upper atmosphere at altitudes of 9-13 km. It was confirmed by a test flight that sample air collected using our system was useful for precise mea surements of the trace gases in the upper atmosphere. Monthly air samp ling was performed over the western Pacific between Narita in Japan an d Cairns in Australia during 1993-1994. Measurements of both CO2 and C H4 in the Northern Hemisphere showed a clear seasonal cycle that was l argely influenced by the seasonal variation in the lower troposphere. A significant decrease of mixing ratio during the winter season was ob served in the CH4 variation, suggesting the intrusion of lower stratos pheric air into the upper troposphere. The seasonal variation of both the gases gradually decayed toward the equator, but a different season al cycle appeared in the Southern Hemisphere. This change indicated th e significance of meridional transport of both gases through the upper troposphere into the Southern Hemisphere. The mixing ratio level of b oth gases showed a recent increase in the upper troposphere.