Large XCH₄ anomaly in summer 2013 over northeast Asia observed by GOSAT

• Main Authors: M. Ishizawa, O. Uchino, I. Morino, M. Inoue, Y. Yoshida, K. Mabuchi, T. Shirai, Y. Tohjima, S. Maksyutov, H. Ohyama, S. Kawakami, A. Takizawa, D. Belikov
• Format: Article
• Language: English
• Published: Copernicus Publications 2016-07-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/16/9149/2016/acp-16-9149-2016.pdf
• ISSN: 1680-7316; 1680-7324

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.<br><br> 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.