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

Abstract

The seasonal variations of greenhouse gases at about 11km 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 50K above the tropopause showed seasonal variations with maxima in November/December and minima in April/May. At potential temperatures of 37.5-50K above the tropopause, SF6 age was estimated to be about 22months in May and 9months 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. Key Points Higher CH4, SF6 at high latitudes in upper troposphere compared to subtropics Larger seasonal CO2 changes at the high latitudes in the upper troposphere Clear SF6 maximum in autumn in LS from tropospheric influences