Composition and Chemistry
Distribution of methane in the tropical upper troposphere measured by CARIBIC and CONTRAIL aircraft
Article first published online: 4 OCT 2012
©2012. American Geophysical Union. All Rights Reserved.
Journal of Geophysical Research: Atmospheres (1984–2012)
Volume 117, Issue D19, 16 October 2012
How to Cite
2012), Distribution of methane in the tropical upper troposphere measured by CARIBIC and CONTRAIL aircraft, J. Geophys. Res., 117, D19304, doi:10.1029/2012JD018199., , , , , , , , , and (
- Issue published online: 4 OCT 2012
- Article first published online: 4 OCT 2012
- Manuscript Accepted: 16 AUG 2012
- Manuscript Revised: 8 AUG 2012
- Manuscript Received: 29 MAY 2012
- Asian monsoon;
- upper troposphere
 We investigate the upper tropospheric distribution of methane (CH4) at low latitudes based on the analysis of air samples collected from aboard passenger aircraft. The distribution of CH4 exhibits spatial and seasonal differences, such as the pronounced seasonal cycles over tropical Asia and elevated mixing ratios over central Africa. Over Africa, the correlations of methane, ethane, and acetylene with carbon monoxide indicate that these high mixing ratios originate from biomass burning as well as from biogenic sources. Upper tropospheric mixing ratios of CH4were modeled using a chemistry transport model. The simulation captures the large-scale features of the distributions along different flight routes, but discrepancies occur in some regions. Over Africa, where emissions are not well constrained, the model predicts a too steep interhemispheric gradient. During summer, efficient convective vertical transport and enhanced emissions give rise to a large-scale CH4 maximum in the upper troposphere over subtropical Asia. This seasonal (monsoonal) cycle is analyzed with a tagged tracer simulation. The model confirms that in this region convection links upper tropospheric mixing ratios to regional sources on the Indian subcontinent, subtropical East Asia, and Southeast Asia. This type of aircraft data can therefore provide information about surface fluxes.