[A-AS11] Stratosphere-troposphere Processes And their Role in Climate

[AAS11-10] Spatial and temporal variations of atmospheric methane concentration and its carbon and hydrogen isotopic ratios in the upper troposphere/lower stratosphere over the Eurasian continent observed by commercial airliner

*Ryo Fujita¹, Shinji Morimoto¹, Shuji Aoki¹, Toshinobu Machida², Yousuke Sawa³, Hidekazu Matsueda³, Yosuke Niwa³, Kazuhiro Tsuboi³, Keiich Katsumata², Takakiyo Nakazawa¹ (1.Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, 2.National Institute for Environmental Studies, 3.Meterological Research Institute)

Keywords:Methane, carbon and hydrogen isotopic ratios, upper troposphere/lower stratosphere, Eurasian continent

Aircraft observation campaigns over the northern high latitudes have been conducted to clarify the spatial and temporal variations of GHGs concentrations and their sources in the surfaces (Sugawara et al., 1996; Tohjima et al., 1997; Nakazawa et al., 1997; Paris et al., 2008); however, systematic time-series observations using aircrafts are still limited (Matsueda et al., 2002; Haszpra et al., 2012; Umezawa et al., 2012). In addition, there is no systematic and simultaneous observation for the atmospheric CH₄ concentrations and their isotopic ratios (δ¹³C, δD) in the upper troposphere/lower stratosphere over the northern high latitudes; except for a few studies using balloon flights and aircraft observation campaigns (Sugawara et al., 1997; Rice et al., 2003; Röckmann et al., 2011). In this study, we have conducted monthly air sampling on-board a commercial airliner between Europe and Japan from April 2012, and clarified the spatiotemporal variations of CH₄, δ¹³C and δD in the upper troposphere/lower stratosphere over the Eurasian continent.
In the upper troposphere, CH₄ concentrations, δ¹³C and δD showed no clear seasonal variations. In the lower stratosphere, on the other hand, CH₄ and δ¹³C, δD showed clear aniti-phase seasonal variations; seasonal maximum (minimum) of the CH₄ concentration (δ¹³C, δD) was found in November to January and seasonal minimum (maximum) was in spring. They can be explained by effective flushing of the lowermost stratospheric air with the tropospheric air in autumn and subsidence of the middle stratospheric air in spring (Sawa et al., 2015). Moreover, compact correlations of CH₄ with respect to δ¹³C and δD were found in the lower stratosphere, suggesting the occurrence of reactions of CH₄ not only with OH, but also with Cl and O(¹D).