Abstract
Abstract. Extremely high levels of column-averaged dry-air mole fractions of atmospheric methane (XCH4) were detected in August and September 2013 over northeast Asia (∼ 20 ppb above the averaged summertime XCH4 over 2009–2012, after removing a long-term trend), as being retrieved from the Short-Wavelength InfraRed (SWIR) spectral data observed with the Thermal And Near-infrared Sensor for carbon Observation – Fourier Transform Spectrometer (TANSO-FTS) onboard Greenhouse Gases Observing Satellite (GOSAT). Similar enhancements of XCH4 were also observed by the ground-based measurements at two Total Carbon Column Observing Network (TCCON) sites in Japan. The analysis of surface CH4 concentrations observed at three monitoring sites around the Japan archipelago suggest that the extreme increase of XCH4 has occurred in a limited area. The model analysis was conducted to investigate this anomalously high XCH4 event, using an atmospheric transport model. The results indicate that the extreme increase of XCH4 is attributed to the anomalous atmospheric pressure pattern over East Asia during the summer of 2013, which effectively transported the CH4-rich air to Japan from the strong CH4 source areas in east China. The two Japanese TCCON sites, ∼ 1000 km east–west apart each other, coincidentally located along the substantially CH4-rich air flow from east China. This analysis demonstrates the capability of GOSAT to monitor an XCH4 event on a synoptic scale. We anticipate that the synoptic information of XCH4 from GOSAT data contributes to improve our understanding of regional carbon cycle and the regional flux estimation.
Highlights
Atmospheric methane (CH4) is the second important anthropogenic greenhouse gas after carbon dioxide (CO2), contributing about 20 % of the total radiative forcing from the major well-mixed greenhouse gases (Forster et al, 2007)
2014 (b) Tsukuba retrievals both at Saga and Tsukuba were observed, reaching almost a same level. This XCH4 enhancement observed at the ground-based Total Carbon Column Observing Network (TCCON) sites is coincident with the high XCH4 observed by Gases Observing Satellite (GOSAT), and strongly supports our speculation that the CH4 rich air was transported quickly from the continent to Japan for this period
In order to see the relationship between the surface CH4 concentration and the enhancement of GOSAT XCH4 over Japan, we analyzed the surface CH4 concentrations observed at three ground-based monitoring stations in Japan, Cape Ochi-ishi (COI, 43.16◦ N, 145.49◦ E), Ryori (RYO, 39.03◦ N, 141.82◦ E), and Yonagunijima (YON, 24.47◦ N, 123.02◦ E)
Summary
Atmospheric methane (CH4) is the second important anthropogenic greenhouse gas after carbon dioxide (CO2), contributing about 20 % of the total radiative forcing from the major well-mixed greenhouse gases (Forster et al, 2007). XCH4 retrievals from SCIAMACHY instrument onboard ENVISAT launched in 2003 was pioneering, but the communication with ENVISAT was lost in April 2012 These satellite data have been used for the inversion studies of surface CH4 emissions. Given the spacing and temporal frequency (3-day recurrence) of GOSAT sampling, along with possible retrieval biases of XCH4 retrievals, it is interesting that the GOSAT detected the synoptic-scale variation of XCH4 that is coherent with the ground-based measurements. This GOSAT-detected XCH4 event suggests the potential of GOSAT XCH4 analysis in higher temporal and spatial resolution. We discuss how capable GOSAT XCH4 is to monitor synoptic-scale XCH4 variations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
