Kazuhiro Tsuboi

Seasonal changes of CO2, CH4, N2O, and SF6 in the upper troposphere/lower stratosphere over the Eurasian continent observed by commercial airliner

The seasonal variations of greenhouse gases at about 11 km altitude were analyzed from monthly air samples collected aboard a commercial airliner flying between Europe and Japan from April 2012 to March 2014. Compared to lower latitudes, the upper troposphere between 50 and 70°N showed higher CH4 and SF6 and an earlier seasonal phase of CO2. However, N2O values were similar to those in the subtropics. CH4, N2O, and SF6 in the lower stratosphere with potential temperature of up to 50 K above the tropopause showed seasonal variations with maxima in November/December and minima in April/May. At potential temperatures of 37.5–50 K above the tropopause, SF6 age was estimated to be about 22 months in May and 9 months in November. This strong seasonal variation is explained by the subsidence of high-stratospheric air in spring and the effective flushing of the lowermost stratospheric air with tropospheric air in autumn.