Aircraft observation of carbon dioxide at 8–13 km altitude over the western Pacific from 1993 to 1999

The spatial and temporal variations of atmospheric CO2 at 8–13 km from April 1993 to April 1999 were observed by measuring CO2 mixing ratios in samples collected biweekly from a commercial airliner between Australia and Japan. The CO2 growth rate showed a considerable interannual variation, with a maximum of about 3 ppm yr−1 during late 1997. This variation is related to the El Niöo/Southern Oscillation (ENSO) events. A year-to-year change related to the ENSO events was also found in the latitudinal distribution pattern of the CO2 annual mean between 30°N and 30°S. The averaged CO2 seasonal cycle in the Northern Hemisphere gradually decayed toward the equator, and a relatively complicated variation with a double seasonal maximum appeared in the Southern Hemisphere. A significant yearly change of the seasonal cycle pattern was observed in the Southern Hemisphere. The impact of a tropical biomass-burning injection on the upper tropospheric CO2 was estimated on the basis of the CO data from the same airliner observation.