Analysis of atmospheric methane from Siberian tower observation using chemistry transport model

Tuesday, 16 December 2014
Kentaro Ishijima1, Motoki Sasakawa2, Toshinobu Machida2, Prabir Kumar Patra3, Akihiko Ito4, Arindam Ghosh1,5, Shinji Morimoto6, Shuji Aoki6 and Takakiyo Nakazawa7, (1)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan, (2)NIES National Institute of Environmental Studies, Ibaraki, Japan, (3)Res. Inst. for Global Change, Yokohama, Japan, (4)CGER-NIES, Tsukuba, Japan, (5)National Institute for Polar Research, Tokyo, Japan, (6)Tohoku University, Sendai, Japan, (7)Tohoku Univ, Sendai, Japan
Atmospheric methane (CH4) is the second greenhouse gas, which is originally a natural atmospheric component, but the amount in the atmosphere has been dramatically increased due to addition of various anthropogenic sources especially after industrialization triggered in 18th century. Such coexistence of both natural and anthropogenic sources at the present make it difficult to quantitatively understand CH4 cycles on the globe. For example, CH4 concentration was increasing in 1990s, became stable in 2000s, and began to increase again from 2007, but discussions on what caused such intriguing long-term variations remain inconclusive. On the other hand, it is well known that wetlands is the largest natural source of CH4. Of them, wetlands in Arctic regions have been recently receiving remarkable attention, because high-latitude regions are more sensitive to global warming than low-latitudes, possibly enhancing CH4 emissions there. In West Siberia, there are large wetland areas significantly contributing to the global CH4 budget. In order to monitor atmospheric CH4 variability, which strongly reflects CH4 emissions from surrounding wetlands, continuous measurements of CH4 concentration from an expanding network of towers (JR-STATION: Japan–Russia Siberian Tall Tower Inland Observation Network) have been conducted mainly in West Siberia since 2004. A previous study on the measurements has revealed that CH4 concentration has large diurnal and seasonal variability, which are driven by seasonally varying wetland and fossil fuel emissions as well as by significant diurnal and seasonal variations of planetary boundary layer height (PBLH). While chemistry transport model can be a useful tool to understand atmospheric CH4 variations in many cases, model simulation for the JR-STATION seems to be slightly challenging, since it is well known that present transport models’ capability to reproduce PBLH is not enough. In this study, we validate model transport of the CCSR/NIES/FRCGC Atmospheric General Circulation Model based Chemistry Transport Model and several types of CH4 emission inventories including a process-based biogeochemical model for the tower CH4 measurements, and try to understand the observed atmospheric CH4 variations.